What it shows
Impression share, overlap rate and position against other advertisers in the same auctions. Useful for spotting a new entrant or a competitor increasing aggression.
The mistake
Treating a competitor’s high impression share as proof their strategy works. Plenty of advertisers dominate auctions unprofitably, for months, before disappearing.
How to use it
As context for a CPC change, not as a target. If your costs rose and auction insights shows a new advertiser at volume, that explains it — the decision is still whether your CPA stays under your ceiling.