Assuming that Hudson's contract has only minimal guaranteeds, Hudson showing in camp and in preseason games that he's not a legit NBA prospect.
Or, KG has a setback and they decide they need another insurance policy in the frontcourt.
All predicated on Sweetney being in decent shape. Before he ate himself out of the league, he wasn't a terrible player. The NY media overhyped him, but an unchunky Sweetney can be a rotation player, not just a benchwarmer.
He's not competing with Williams; Sheldon's here for the year, they aren't going to cut him. Assuming no trades, it's competing with Hudson and perhaps Tony Allen. If Tony's still hurting and they really think both Hudson and Sweetney are worth keeping around, I'm wondering if they might come to some kind of injury settlement with TA.