My most fav VNAV observation that tells me instantly that it is not understood goes like this. "I'm starting down early to get a head of the path." Ok says I and nobby promptly selects DES NOW or mashes that there altitude selector. We now start a shallow descent and THR HOLD presents itself. We continue on that 1200 ish fpm descent until re intercepting our original flight idle descent path that was 40 miles in front of us when we started down on this oddisy. The TLs go to IDLE and "What did we just accomplish" says I to a blank stare.