I try to do it every year---if it's dry enough.  Usually run a Blu Jet subtiller 14-15" deep at the V3-V5 stage.  If you set it right, it doesn't lift the corn at all, using summer points. It helps corn root down deeper and helps stave off a hot, dry spell longer.  Lot's of times my neighbors' corn is rolling and mine isn't.  Always gains me 7-20 bushels in side-by-side tests.  I've done enough testing that I just run it on every acre that I can.  In fact running the inline ripper has gained me more bushels than adding another 40-50 units of N as side dress.