Because I couldn't be bothered remembering to switch them off every night (and have never done this on any other phone).
Again, this is not about "overnight", it just so happens that overnight, when I'm not actually using the phone, is the best time to try to figure out what is eating up my battery.
I'm also not actually complaining about the battery life on the S6 (I ain't a hater!). I was just curious why the phone would go through about 12-15% battery when I wasn't actually using the thing overnight.
I hear ya. Yeah, for me, I've always noticed how wifi on, location/gps, (and bluetooth probably) can burn battery life so I only ever turn those on when they're actually needed and then turn them off. I'm guessing you keep yours on all day?