I like to wear sandles when jumping for several reasons. The first reason
is the takeoff is usually not really smooth and soft. Instead,
there's usually little sharp rocks and pebbles to slip on. These
provide some nice traction at the takeoff. Secondly, since you
usually land feet first, these will save the bottoms of your feet
from a nasty slapping. It really hurts to jump and land barefoot.
And lastly, as you're climbing back up to go again, its nice to
have these instead of trying to scale rocks barefoot.