There's many accessories that rely on bluetooth nowadays: smartwatch/smartband, headset (moreover with the newest trend of ridding the 3.5 mm jack), etc.

I used to do that, but my new phone has better batteries, so that isn't an issue any more. Combine that with my bluetooth headphones, and it's more convenient to just keep BT on at all times.

It's easy to forget. I probably leave my phone's wifi hotspot on accidentally about half the time too.