The efficiency of having your hands in home typing position is ergonomically un-parralleled. The keyboard is designed with the average persons fingers reach in mind, and hence you make the largest amount of realistic keys immediately availible to you by doing so.
Even moving over one or two keys more to RDFG, or THFG then makes your tab and caps keys less then easily reachable, so moving for one more row of keys is purpose defeating.
If you like it, cool, use what you want, but the only good reason I've heard for doing otherwise (logically speaking), namely WASD is if you have an abnormally small hand and can't functionally reach certain keys or combinations there of from home position, like left ctrl/shift, especially with that pesky windows key down there.