While the basics of what OG says is true, there's a bit of a caveat there. Not every JC recruit has used his RS year. If that's the case, we can bring him in, RS him, and then have two good years with him later. Or, we could put him on a modified Garrett White plan: play him a year, and if he's having problems that a RS year can help with, let him use his RS after his JR year, and then have one more year after.
One benefit of JC recruiting is that if you have a personnel issue in dire need of a quick fix, one top-notch JC guy can fit the bill. But one very large drawback is the fact that if you over-do it with the JCs, you're going to have more frequent turnover, which can cause chemistry problems, not to mention identity issues at the gate: if the fans don't recognize the players because they're roatating through so quick, they might not come. In that regard, having a good HS recruiting basis is key, using JCs to fill in holes here and there. Of course, if you find a worthy kid looking for a second chance (one of those 4-2-4 guys), you give him a chance. But in general, I say focus on HS recruiting, and use JCs to fill in holes.