In most cases, you’re going to choose a Facebook campaign objectiveWhen you create a campaign, one of the first things you'll do is select an objective. The campaign objective is your ultimate goal. Your selection will impact options, including optimization and delivery. Options include Awareness, Traffic, Engagement, Leads, App Promotion, and Sales. More related to a specific type of action (conversionsA conversion is counted whenever a website visitor performs an action that fires a standard event, custom event, or custom conversion. Examples of conversions include purchases, leads, content views, add to cart, and registrations. More, store traffic, engagement, app installs, etc.). But there is a time and place for using the ReachReach measures the number of Accounts Center Accounts (formerly users) that saw your ads at least once. You can have one account reached with multiple impressions. More objective with Reach optimizationTo access Reach optimization, use the Awareness objective and "Maximize reach of ads" performance goal. Reach optimization allows you to show your Facebook ads to the maximum number of people while using a frequency cap. More.
Let’s discuss…
Reach Objective Defined

The tip Facebook provides for the Reach objective is simple:
Show your ads to the maximum number of people.
This is an important distinction. In most cases, you want Facebook to show people to a small percentage of people in your target audienceThis is the group of people who can potentially see your ads. You help influence this by adjusting age, gender, location, detailed targeting (interests and behaviors), custom audiences, and more. More who are most likely to perform your desired action. By choosing the Reach objective, you’ve indicated that the action isn’t so important; you want to get your ad in front of as many people as possible.
This happens ad the ad setAn ad set is a Facebook ads grouping where settings like targeting, scheduling, optimization, and placement are determined. More level with optimizationThe Performance Goal is chosen within the ad set and determines optimization and delivery. How you optimize impacts who sees your ad. Meta will show your ad to people most likely to perform your desired action. More.
Reach Optimization Defined
The Reach objective is unique because of what you can do at the ad set level related to optimization.
Your only options for optimization under this objective are Reach (the default) and ImpressionsImpressions are the number of times your ads were displayed to your target audience. Impressions aren't counted if it is detected they came from bots. More.

Reach optimization is what ultimately carries out the Reach objective to serve your ads to the maximum number of people.
You can then set a frequencyCalculated as (Impressions/Reach), Frequency is a Facebook ads metric that measures the average number of times users have seen your ad. More cap, which limits how often you can reach people.

The default is 1 impression every 7 days. If that’s what you use, you’ll need a very large audience or low budgetA budget is an amount you're willing to spend on your Facebook campaigns or ad sets on a daily or lifetime basis. More. Ultimately, though, it’s going to depend on why you’re using Reach in the first place.
Reach vs. Reach and Frequency Buying TypeThere are two buying type options when determining how you will pay for a Facebook ads campaign: Auction and Reach and Frequency. More
Don’t confuse this option with the Reach and Frequency buying type. When setting up a campaignThe campaign is the foundation of your Facebook ad. This is where you'll set an advertising objective, which defines what you want your ad to achieve. More, most advertisers will use the AuctionFacebook uses an ad auction to determine the best ad to show to a person at a given point in time. The winner of the auction is the ad with the highest total value, based on bid, estimated action rates, and ad quality. More buying type, which is selected by deault. But, you can change it.

A full explanation of Reach and Frequency buying requires a separate blog post, but a few things…
First, you can use Reach and Frequency buying in connection too multiple objectives (Brand Awareness, Reach, Traffic, Engagement, App Installs, Video Views, and Conversions).

So, that’s a potential advantage over the Reach objective and optimization in that you can choose to optimize for a specific action while still using frequency cappingFrequency capping allows you to limit the number of times your audience sees your ad during a given window of time. More.

You’ll also get predictions related to how your ads will be distributed.

Where this starts becoming less accessible for all advertisers is that, at a minimum, you need your campaign to reach 200,000 people.

That may mean spending more than smaller advertisers are comfortable with.

This is intended for broad targetingIn most cases, mention of Broad Targeting refers to the removal of all potential targeting filters: No custom audiences, lookalike audiences, or detailed targeting. Instead, rely only on location and letting the algorithm do the work. More within a single country. While it technically can be used with custom audiences, that assumes those audiences are big enough to reach your minimums within a country.
In other words, Reach and Frequency buying makes sense for a small segment of advertisers.
Reach vs. Daily Unique ReachDaily Unique Reach Facebook ads optimization allows you to limit the number of times you reach your audience to no more than once per day. More
Another option to compare this to is Daily Unique Reach optimization.

Daily Unique Reach has actually been around longer, but it’s more simplistic. Reach allows you complete control of frequency capping; Daily Unique Reach simply caps reaching people no more than once per day.
That’s the big advantage to using Reach optimization. It’s the happy medium between Daily Unique Reach and Reach and Frequency buying. Granted, I’d prefer to use Reach and Frequency buying for smaller audiences and lower budgets, but Reach optimization is the next best thing.
Use Cases for Reach Objective
Reach optimization solves a specific problem for me. There are times when I want to reach as many people within a small audience as possible. And it’s nice to be able to frequency cap.
This is the way I pull off my evergreen campaigns. I have a small group of people whom I want to reach — and I want to reach all of them if I can. I use short durations and high frequency cap limits to reach them during a short window of time.
When using Reach, though, be careful regarding how you spend those limited impressions. I choose a select couple of placements so that I don’t waste impressions on Audience NetworkAudience Network is a network of mobile apps that have been approved to monetize their apps with ads. This is how you can show your Meta ads to people while they are away from the Meta family of apps. Audience Network and associated groups are among your placement selection options in the ad set. More, for example.
Overall, it’s up to you. Get creative. Test it out!
Your Turn
Have you used the Reach objective and optimization? How have you used it, and what kind of results do you see?
Let me know in the comments below!