He'd get some looks coming from doubles on Cousins or Gay, better shots that JT may not be serviceable to do. Collison would find him for a shot or two that is not really a threat area from JT. He'd also be able to slash and drive. He should only take maybe 2 threes a game, just to keep people honest away from the key, and only take uncontested ones.
But Smith is expensive, that's a hefty investment. You either gamble that investment pays off, or gamble JT can man up like this an entire season and we reinvest the salary difference between the two of them next season. We may be better off keeping the cheaper JT and looking for a SG now instead of loading up with Smith.