I use reach and impressions at different times in my campaigns. Others have stated that Cost Per Action is what you should pay attention too. I agree.
Others stated that Reach and Impressions is only for large brands, and to an extent it may be true.
There is a “reach” campaign objective, as well as a daily unique reach optimization objective within the conversion campaigns. There is no “impressions” campaign, so Im assuming you are comparing the optimizations available under conversion or other campaigns vs actual campaign objectives.
There are specific cases for each within a larger campaign.
When I use impressions:
I work with a number of different type of clients. In each case we run some type of retargeting and reminder type of ads within a conversion campaign.
This might be a video views campaign where we retarget only XX% viewers with an offer. Or it may be retargeting only people who get to the checkout page and haven’t purchased yet.
For the generally smaller audiences (10’s of thousands or less) who have already performed some action, I want to get an ad in front of them to move them through the funnel.
I want them to see an ad even if Facebook wouldn’t show it to them in a normal conversion optimized campaign.
When I use impressions, I show the ads to a specific set of people as often as possible for a set period of time. This is usually for a launch or a specific amount of days.
I only use this type of optimizations inside of a conversion campaign. An asset will still be optimized for a particular conversion, like purchase, but where I can adjust the budget and optimization, I’ll choose impressions.
In these images you can see the estimated reach that a particular asset is going to get with conversion vs impression optimization. This particular group of less than ten thousand people had a 49x return on ad spend so I even a few hundred more impressions per day made a big difference.
(Same budget in each)
When I use Daily Unique reach:
I use daily unique reach optimization, inside of a conversion campaign when the campaign is already performing at an extremely high rate.
For example If I have an ad targeting a normal to larger cold audience (1Million or larger) and the click through rate is over 5%, for a few days I will test daily unique reach optimization.
Basically, enough of the audience is going to click the ad anyway, it doesn’t need the Facebook algorithm to find the right people. So I’d be looking to show it to as many people within the audience as possible. I’ll still be keeping an eye on the Cost per action.
Here is an example: (Same budget in each)