Most people leave Bluetooth _on_ all the time, because they’re not thinking about the technical nuances of marginal power consumption - instead they’d rather just leave it on for convenience.
The only Bluetooth disabling I do is ensuring the car’s stereo doesn’t try to connect to my phone. Having a conference call switch mics to the sound of momma yelling at the kids when she starts the car is...undesirable.
The only bigger consumer of a cellphone's battery is the Facebook application. Trust me. People know what eats up their cellphone battery and they turn that crap off as much as possible.