There is a big difference between 'it's not necessary to do that." & "Do not do that." In the former it is your choice if you want to spend time, cover your back-side, have fun, feel superior etc. etc. In the latter....clear & simple.
For AB guy; it would seem odd to have an FCOM/video telling you to hand spin the engine on an AB and not to do so on the very same engine on a B737. Surely it is an engine thing not an aeroplane thing.
I was taught to do it on PW JT-8's, first flight of the day, especially in winter. It could have been sitting out there for a few days in freezing conditions. And why not? 2 secs of hands on and bonding with your engines. Give the spinner cone a kiss if you can reach it. Hug the radar dome on a TS day: whatever floats your boat. None of it is a "Do Not."
For the engine spinners: do you do it forwards or backwards? Let's get to the important nub of the matter.
