I leave mine on all the time but put it on airplane when not using. If i knew i wasn't going to use it for a couple of days i would probably power down.
To answer your query: if I'm not using the WiFi why should I let that drain my iPP's battery? Makes sense to shut that and bluetooth off when I am not using it (like now.)
Yes for me I have noticed a small difference it battery life shutting those two things down. Also I don't want to be tempted to pick it up if I can't sleep. I just watch tv instead. I know it makes no sense but hey it works for me.
I have an iPad Pro at work that I haven’t used all week. With Bluetooth and WiFi enabled, it was at 94% when I opened it today. Not too worried about battery drain.
That’s how they are engineered. There are no moving internals which are suspended when not in use. Also, Apple never says in any documentation to power off.