Google has launched a target frequency feature for YouTube campaigns, allowing advertisers to control how many times an ad is shown. Previously, this level of control over ad frequency on YouTube was only possible for advertisers running connected TV campaigns in Google Display & Video 360. Now, the target frequency capability is available for all advertisers running YouTube campaigns. Google understands that it is frustrating for viewers to see the same ad multiple times and that it is not effective for advertisers to have their ad played frequently. A study that Google commissioned found that the return on investment for TV advertisers decreases by 41% when the frequency of the ad being played exceeds 6 times per week, which represent 46% of TV impressions served. According to Google, almost all (95%) video reach campaigns that followed recommended best practices achieved their desired frequency goals. Target frequency is a feature available to all Google Ads advertisers worldwide. To set up a frequency-optimized campaign, create a new video reach campaign and set the goal to target frequency. Then, select the desired weekly frequency.
(source: https://www.searchenginejournal.com/google-rolls-out-ad-frequency-targeting-for-youtube-campaigns/470790/)