I have shot quite a bit with a lens. Benefits are a slightly bigger target. For some 3D applications this can be helpful, but the drawbacks would prevent me from ever using it for hunting. Drawbacks are that they suck in the rain, if it's sunny they can develop a glare, your range of movement is magnified, and sometimes POI moves if you have to take the lens out for emergency purposes in the rain. Also keep in mind unless you are shooting in sanctioned ASA shoots, no other organization that I know of and most local shoots will bump you into open/open pro class for 3D if you have a lens.

With that said, when I shoot open stakes for 3D, indoor spots, field or FITA I do use a lens on a Copper John Ants sight, but for anytime I am using a pins sight I do not.