I generally dial elevation for each target (except on holdover-only stages), and rifles/scopes tend to get bumped against barricades and props, going in and out of narrow openings while on the clock and trying to hurry, etc. I even had a rifle in a stand get accidentally (or was it?!) kicked over onto concrete by a guy. Luckily, the Bushnell XRSII held zero even after a direct impact on concrete while aboard a 15 lbs rifle, and continued to function perfectly throughout the rest of the match. Even just the recoil of 100 shots per day over many days of competition, a lot of driving on gravel roads, etc., can (and does) cause zero shifts.
Most of the Leupold guys are holding with the reticle rather than dialing, so that mitigates the RTZ and tracking problem, for the most part.