First off, many people believe that Bennet will play small forward for the Cavaliers. Personally, I disagree. I don't think Bennett is quick enough laterally to defend small forwards. I think that Bennett can actually be a very effective stretch power forward in the league. Watch the following video to get a better idea of Bennett as a player:
Bennett is super versatile, and he can operate as a post-up player, three-point shooter, and elbow-driver. He has great form on his jump shot, and it seems likely that he can become a pretty good shooter in the NBA (at least). Bennett is also pretty explosive, and can blow by defenders and dunk on them with ease. His post moves are weak, but with a little work, he can become a solid post-up player. He can drive effectively from the elbow and short-corner area. His biggest strength is his finishing ability, as he converted a ridiculous 74% of his attempts at the rim during his freshman year.
Why can't he be a small forward?
Well, although Bennett is athletic, he doesn't possess the fluidity that you would want from your small forward. Bennett is quick, but he's not smooth. On his drives to the rim, he gets by his defenders because of a combination of his tremendous strength and quickness. However, he looks very rigid, and often relies on straight-line drives to get to the hoop. In the NBA, defenders will be much stronger and quicker. If Bennett wants to convert to a wing, he will have to improve his movement ability and ball-handling skills. While Bennett is fast and athletic, he's not "small-forward" fast and athletic.
At power forward, Bennett can be an absolute nightmare. Think Charles Barkley (who stands at like 6'4'' to 6'6''). The league has gotten much smaller, and at the 4 position, Bennett can overwhelm opponents with his speed and strength. His outside shooting will make him a match-up nightmare. If he develops a solid fadeaway jumper and right hand jump hook, he will be very hard to guard. Bennett's strength and long arms will allow him to pull down many rebounds (despite his lack of height). His defensive effort at UNLV was also lacking. In the NBA, Bennett can become a great defender if he puts his mind to it.
Overall, Bennett is a great pick. There are many people who think that the Cavs should have taken Nerlens, but the more and more I look at it, Bennett seems like the right pick. He fits in with what the team needs. Additionally, he will actually improve the Cavs offense. With Nerlens, the Cavs would have little offensive improvement. Bennett clearly wants to be a full-time wing, but he would be better suited to use his athleticism at the 4 position, where he would actually be a mis-match. When looking at Bennett, a former player by the name of Derrick Williams comes to mind. Williams has not lived up to his high draft pick, and a lot of that reason hinders on his position change to small forward. Bennett is a stronger (physically and skill-wise) prospect than Williams, but he should be wary of the dangers that come with such a dramatic position change.

