It probably isn’t a noticeable amount of the course of a day - but if the hotspot is enabled then it’s continuously shouting from the rooftops “Hello, I’m an access point! My name is ‘Djhorn18’s Phone’ You can connect to me if you want!”

Which it wouldn’t be doing if it was off.

That being said I’ve kept mine on all the time and never have any battery issues with any device I’ve owned. Android or iPhone.