Leslie would give LSU a mature big WR with deep speed. I'm not saying that he is Randy Moss, but Moss used to give defenses all kinds of fits. He caused teams to start rolling their cover to his side. We need that type of threat to open up the passing game and it would also create more running lanes.
I'd temper my excitement on Leslie. The kid has a reputation for needing to learn how to work on his game. He did not lead his juco in receiving as a soph. (he did in yards, but far from it in catches) which spoke to issues with consistency in route running beyond just the "go" route.
When he gets to BR, he's going to have to up his work ethic level two or three notches and learn to pay attention to detail.
If he does all that, then he'll be very good.