The only time I crank it up beyond 21 in the dry sand is when I think it may help me identify a deep weak signal. I just don't like a bunch of continuous chatter. I run 21 in the sand....beach low conductors and 19 in the water.... surf and seawater mode. There's some chatter, but not too bad.
I think if you run it too hot, the chatter could possibly mask some target sounds. Also, a lot of people say higher sens make's ID #'s less reliable/jumpy.