Bluetooth is slow. The transport is 3Mbps at max, if you subtract all the headers from different layers, you may have like 1.5-2Mbps practical transfer speed.
Sounds like the "or such" wins, but even with bluetooth speeds that means you're backing up 1-5 photos per minute and that helps a lot.
And harm a lot too, you phone can't deep sleep since it has to wake up periodically to process data from bluetooth stack. Combined with slow transfer speed, that gonna eat your battery like nothing.
Playing audio over bluetooth also wakes things periodically, but it uses almost no power. With a similarly competent design photo transfer should be very battery efficient.
No, most(if not all) bluetooth controller has audio offload, basically the cpu does not involve(or very little) when transfering data from storage to radio.
Don't you mean yes bluetooth controllers have audio offload? "similarly competent design" means you do the exact same thing in the other direction. Instead of rarely waking up the CPU to coordinate sending, you rarely wake it up to coordinate receiving.
WiFi is a little faster I guess? In the primitive days people used the EyeFi.
You would often not have wifi available, and you wouldn't want to have to type in wifi passwords to your camera all the time. But your phone will almost always be nearby and persistent bluetooth is easy.
Wifi between your camera and the phone. Or your camera and a laptop in your bag or whatever...
Problem is they have to disconnect from the current wifi ap to connect to the cameras ap which is inconvenient and means there can’t be a constant connection.
Wifi NAN could be used to solve this problem but I’ve not seen anything using it. Apple only just added support last year though.
They do transfer, but it's not automatic.
My Nikon ZF transfers to my phone through Nikon's SnapBridge app automatically.
Oh, that's cool, kudos to Nikon, could be a good reason to switch over from Fuji.