Video viewers are a custom audience in the Facebook Business Manager, and custom audiences are what make Facebook ads so effective (and Facebook so lucrative as a company). These audiences’ behavior has proven that they’re interested, and remarketing to them can help you take some of the guesswork out of your efforts.

Other Facebook custom audiences include:

Lookalike audiences. These are the holy grail of custom audiences, in my opinion. These users are new to your business, but based on the 52,000 data points Facebook has, have historically behaved similarly to another audience you identify (users who like your page, for example, or past buyers).