Winterizing question

I searched the forum for past posts and read most of them on winterizing. My question is this...the TM manual describes draining everything, removing the heads and a little antifreeze in the sink traps (if you want) as winterizing. Nice and simple, I like it. But reading thru the posts here, people are pooring 3 gallons of antifreeze into the fresh water tank and pumping it thru the system. Is this really necessary? Why the big difference from the manual?