Phillies know they rushed Rojas and Kemp due to injuries. Both could have used a full season in Lehigh.
Which may explain why they've resisted the temptation to recall Crawford, even though he's raking.
There's a tough balance between allowing a player to succeed at a lower level and challenging them.
Probably the easiest is promoting hitters from JS to Reading, because the higher level of play is balanced by a friendlier ballpark - but the opposite then holds true for pitchers.