As I've written numerous times, I think most players strongly benefit from a year at each minor league level. Many teams like to promote players directly from Double-A these days, but I think in most cases it is a bad decision. Double-A and Triple-A teach different lessons, and skipping the latter often backfires.
That said, there can be exceptions at times, and Jeremy Hellickson of the Tampa Bay Rays could be one. He's currently 11-2, 2.21 with a 104/26 K/BB in 106 innings for Triple-A Durham, 94 hits allowed, 2.61 FIP. The guy is just a monster; his minor league career record is now 45-15, a .762 winning percentage....yes I know wins are not a predictive stat, but c'mon: .762? You have to be impressed with that. He has a 2.62 career ERA, and a 611/126 K/BB ratio. He's given up just 462 hits in 567 innings. His career FIP is 3.11, and has been over 4.00 just once in his career, during the second half of 2008 in his first exposure to Double-A. Statistically, it is hard to be better than Hellickson. Scouting-wise, he may not throw 100 MPH, but his stuff (89-93 MPH heater, plus changeup, good curve) is solid and his feel for pitching and aggressiveness are first-class.
At this point, there is no real pressure to promote him. The Rays rotation is healthy. David Price and Jeff Niemann have been excellent, and Matt Garza has been pretty good. Rookie Wade Davis has been ok, not great but not bad enough to lose his job at this point. James Shields has an elevated 4.87 ERA, but has maintained a good K/BB ratio and his spot doesn't seem in jeopardy. It seems quite possible that both Shields and Davis could do better in the second half. The Rays are also conservative about promoting pitching prospects, and like to give them a full year at each level, the same philosophy that I expouse.
The Rays are just two games behind the Yankees and lead in the wild card standings. But let's say that as August approaches, one of the starters gets hurt, or Davis implodes, or Shields' luck doesn't rebound and his ERA creeps over 5.00. If you really need another starter, would you pull the trigger, promote Hellickson, and stick him in the rotation for the stretch run? Or would you stick with the development program, keep him in the minors until September, and give Andy Sonnanstine a chance to start again?