They are supposedly beneficial, but I like knowing that when I stick my hand in the tank, that they're not looming under some rock. I remove the ones I've found. Maybe if you don't wanna kill it, just toss it in the sump.
I like to have them. The scavange, which is good because they remove any wast. Ive also seen them eating algae off of the glass, which is good.
The only negative I can think of is that pol don't want to get "stung" by touching them and having bristles stick in their fingers. Ive had it happen and it was no big deal. Also, you should be wearing gloves anyway, so it's a moot point!