Sorry I'm late to the party
. In my younger years I was an avid caver and rock climber, and Prusik knots were one of the handiest knots in my bag of tricks, but there are some downsides you need to be aware of.
First, they don't work well on wet, muddy or icey ropes. Your descent under those conditions is more a barely controlled fall. Prusiks can also be really hard to release when wet.
If you're using a single Prusik on a safety line, be aware that you can't release the knot while it's bearing weight.
The heavier the weight, the tighter the knot grips the rope, so unless you have some means of taking your weight off of the knot, you'll probably find yourself just hanging around for awhile
Finally, the rope used to tie a Prusik must be a smaller diameter than your climbing or safety rope. If not, it can't grip the rope very well and you'll take an express ride to the ground. Here
is a decent article with a lot more information and diagrams.
The best advice I can give is to practice using these knots under controlled conditions, preferably with an experienced climber, before you use these in the field.