I just left mine sticking out, less breaks in the wiring is always preferable although plates do have that finished look if they are going to be exposed behind the speaker. I used a stainless steel wall plate that I had drilled in the middle for the wire to protrude with a nub to hang the Defintive Technology bipolar surround, which has a keyhole on back. The speakers fit flush with the wall so you cannot see the plate anyway. Whichever method you do just make sure any wiring run inside walls is CL3 rated for fire retardent properties, in some places it is code.
I decided to use wall plates because (1) I wasn't sure how much wire I would need coming out of the wall, and (2) with wall plates the unattractive cheap wire can be completely inside the wall and good looking wire attached to the banana jacks or binding posts outside.
I soldered the in-wall wires to the backs of the binding posts, eliminating some of the possible oxidation problems at connections. So each banana plug would have just two joints, from the exposed speaker wires to the back of the plug and the plug itself in the jack.
For wires coming through a metal wall plate, a grommet or bushing is needed so the rough metal edge of the hole does not cut into the wire.