I always thought there had to be some sense of 'oomph' somewhere in the swing but Puttmad's coments have me re-thinking this. uummm.
Any "oomph" must be initiated at the top, or sometimes even before...it takes roughly 1/3 second from the top to impact....for most of us (not all), any command to stimulate any set of muscles must be made at the top (ish) in order for the muscles to have time to fire before the club comes down to the impact position...
There are exceptions to this however, eg there is an Israeli policeman who can snatch a gun from someone pointing it in his face and reverse it and shoot the guy in under 1/3 second...but he has done daily training all his adult life....
This is why the "late hit" fad a few years ago was such a failure...by the time your body tries to command and react so late in the downswing, you are way past impact and basically trying that move will usually throw you right off balance (usually falling onto the back foot)....now there's nothing wrong with a late hit, my problem is with the way it was "explained" and "taught"...