You could essentially run a 3 guard rotation of Conley/Mitchell/Exum in the playoffs if you're worried about the size discrepency on the defense end, since the flaws in Exum's game are covered up by Conley and Mitchell's offensive prowess while Exum gives the Jazz the length and size at the guard spots to guard bigger guys like Harden. You could probably also get away with a 3 guard lineup against a team like the Rockets if they go super small and have Exum on Harden, Conley on CP3, and Mitchell guarding whoever the wing shooter they have.
Realistically speaking the main reason why Exum didn't play as much as he probably should have in the playoffs last year was because he coughed the ball up seemingly every possession, which was a shame because he was quite clearly a difference maker defensively when he was tasked with guarding Harden. If he can play the way he was prior to the injury on the offensive end while providing the elite man on man defense he can bring then I think he's a key bench piece for the Jazz going into the playoffs and just as important as Crowder off the bench.