Benefits are numerous. In fact I can't think of any downsides. Main idea is that they are part of the base of your tanks ecosystem. Many fish in an aquarium will use them as food and some require a diet of nothing else (some species are hard to ween onto frozen food).
The best way to keep a good population is to have a refugium. Mine is in my sump however there are HOB
refugiums as well. It's a place of "refuge" for them to hide and thrive. I put some varieties of algae and live rock in the refugium and this seems to keep them happy plus it's extra biological filtration