With the exception of some DH forks/shocks, rebound settings only effect the low speed end of the rebound control. High speed rebound control is set internally in the shim stack. So this effects how bike bike feels after a deep slow hit, g-outs, high force berms and rider input. Basically you can’t go far wrong with setting it too slow. Contrary to alot of advice I tend to set bikes so when you push down on the forks/rear shock they feel a similar speed (but very slow). The worst that’ll happen is packing down, which at the end of the day makes it at worst feel like a shorter travel bike. I find that only happens on parts of a track where poor performance of suspension only effects comfort, not speed. The slow rebound produces real benefits for stability where grip is limited.
Don’t forget that a fast bike setup won’t always be the setting that makes it feel comfortable.