In-app bidding (sometimes called header bidding in app) replaces the sequential waterfall with a unified auction. Each bidder values the specific impression, so prices reflect the user and context rather than historical averages, and latency falls because calls happen in parallel.
Bidding improves competition but does not remove the need to inspect delivery. Bid rate, win rate and show rate still vary by network and placement, and fill often rises before revenue per eligible opportunity does.