A frequency cap limits how many times a single user sees the same ad within a defined time period for example, no more than 3 impressions per user per week. Without a frequency cap, algorithms optimizing for conversions may repeatedly target the same person, causing ad fatigue, declining CTR, and negative brand sentiment. On Meta, frequency is especially critical for retargeting campaigns with small audience pools. A rising frequency metric alongside a falling CTR is the clearest early signal that a creative needs to be refreshed or the audience expanded.