Normally one assist hook can be used both for bigger and smaller targets and also it can be used in two siyuations. The first option is to use a big assist hook with a curve much wider than the width of the jig. This combination is targeting mostly bigger fish with large mouth like groupers, Amberjacks, leerfish etc. Those fish normally attack and gulp the whole jig so the single large assist hook for sure will have a good chance to hook on the interior of the mouth and the wide curve helps a lot for succeeding this. The  other portion is to use a single assist hook on short jigs that the width of hook is equal, slightly wider or even narrower that the body of the jig. The important thing is not to able to snag on the jig body and move freely at all times. A wide and big single assist hook serves us better than we deal with big fish. The thick and strong body of the hook guarentees a deep secure hold on the flesh or even jaws of the predator's mouth or body. This allow us to pull hard with drags set in very high power and even stop a big group from run to a cave. 

S2 Ocean Smart Assist Hook M&W