Said with such authority, but wrong.
So if you look at the original post, he says that it saves his phone from switching between EDGE and 3G, which tells me he has a really bad phone signal.
While switching to Wifi won't help that (the phone will still be hunting) perhaps it takes him less power to use wifi for data in such circumstances.
If you don't have active data going, like push email, IM, etc, clearly this won't do anything.
Personally unless I'm streaming music, I never switch to wifi.. It is a little easier on battery than cellular with streaming music however. Otherwise, nah.