Impressions per Period is used to limit the amount of impressions per placement for a period of time. E.g. one can limit it to 10 impressions every 3 hours. It means that if there have been 10 impressions in the first 5 minutes — no ads will be shown until the current period (3 hours) expires. Thus, game balance can be regulated.
Impressions per Period Setting
How to limit the amount of impressions for some placement
Written by Tanya Moroz