I'd disagree with this, sorry. I found out the hard way (a pod of 5 dolphins swan past me about 10m away) that taking shots on and off consumes battery faster. After that I record the entire dive, usually switching on after descent and clearing my ears. I dive holding the camera at 90 degrees most of the time and then if there is anything I actually want to shoot, I turn the camera round properly. I mark the end of the shot by waving my hand across the lens, though not too close as this affects the auto focus, and put it back in the 90 degree position.
What I then have is 40 mins or so minutes of footage, most of it is rubbish with the seabed horizon running vertical, mask clearance etc but then it's easy with a video editor to pick out and segment the proper footage.
To completely contradict myself, I have now found myself turning off the record if there's particularly bad viz, bad light or just not much to see. Or if I've shot shot something pretty special in the last 20 mins and don't want to risk jeopardizing the footage. But even then I'll still record in 15-20 minute sections and usually record most of the dive.