In an ideal world everyone you have on the roster should be able to step in and play a major role at a moment's notice. In an ideal world you would stack the bench with All-Star level players and slot them in and out as needed NBA2k style. The problem is that players aren't machines, they are human beings with goals and aspirations for their jobs, like everyone else. End of bench is really about fit to me. Will those players be happy with zero to minimal playtime that may happen irregularly, at a moment's notice, because of an injury or something else? Do they have the skills to contribute? Will they be happy to go back to that bench role after the player they replaced comes back, even if they had played well? Will they expect more and be unhappy if they don't get it?
That's that hard part about getting overqualified players for bench roles. They can start to disrupt chemistry, especially if they are charismatic, opinionated or have an illustrious past in the game. So managing the fit in the team becomes really important. If they're going to be a cheerleader or an insurance guy or a practice guy, make it crystal clear to them that that's what they will be. The draw would be the chance to be on a championship team and contribute to it in their particular way.