Primary creator on the bench, will defend wings. Allows Mills/Joseph + possibly Denmon to defend PGs and not have to be creators (not their strengths).
Will struggle to defend initially (like basically all rookies) but will rebound really well. Conditioning/athleticism is an issue, should improve over time- Fat is potential in disguise so should get better defensively as he trains better (Jordan Adams was also tubby, UCLA might just not be great at getting athletes in optimal condition) and ages. Has length to make up for lack of athleticism against most backup SFs(I'd guess this is the position he defends). Not a huge issue as we have a decent SF now and in the future to defend long wings/4s (Kawhi, Livio) and Green can cover well.
Unlikely to play a ton as a rookie. Spurs will continue to rest Manu and Mills/Beli/Slowmo will play a bit as bench perimeter trio.