So this thread is obviously a bit of a joke. Keeping your head down is probably one of the most overused cliches in casual weekend golf instruction.
Blehnhard mentioned the parallel neck location and impact which is absolutely true...but I wasn't even trying to be that clever.
So why did I start this thread? Because I was at the range the other day and some random guy suggested that I should try to keep my head down. On one hand I was thinking "stfu and get back to hacking balls you inbred cream-puff", but being a reasonably open minded person I decided to give this tip a go. And it worked. The pulls I was hitting that day disappeared.
What's my point? My point is no matter how rubbish something sounds, it will work for someone out there. The teacher's job is to find the simplest "tip" that will "fix" that person immediately. The change may just be a stepping stone to additional upgrades in the future. Also, something can be scientifically unsound, e.g. the heavy hit, sustaining the lag, etc., but yet produce great results. And something can be very scientifically sound but yet produce poor results. I'm sure members here can find examples of each.