I spend several minutes a day doing kegels. I've been doing this for probably more than five years. I haven't noticed any miraculous changes, just slightly better erectile quality and better over all control.
As with any exercise, you develop more strength, endurance, and coordination, and it acts as a way of slowing down the aging process.
I've always been more oriented toward delayed ejaculation, not cumming as soon as I would like, and I've found that being able to contract the pc muscle forcefully often enables me bring on an ejaculation relatively quickly when I want to do so, probably because it puts some kind of pressure on the prostate.