If it were not for my GoPro I would have no photographic / video evidence of my time underwater. I don't love photography - it is something I do to capture memories. As I discovered when my kids were young, though, looking through the lens of a video camera is not the same as actually experiencing the event.
I dive not to take video, but to enjoy the experience. A head mounted camera allows me to capture it relatively unencumbered, without thought or effort. I do not have to remove my self from the moment to focus my attention on operating a piece of kit.
If the video turns out less than perfect, its "loss" cannot take away the experience I was immersed in.
With a hand held camera, if I "lose" the video (really lose, or it just doesn't turn out well) I lose not only the video but also miss out on the experience. Even if the equipment only requires minimal attention, it is still a distraction, one that I don't want.
I added a chin strap to my GoPro and have captured numerous dives with zero effort. I position the mount pretty much in line with my hood opening, which allows it to clear my mask. If no hood, just a hair above the mask. I have not marked it (EDIT: here, I mean the angle, not the initial position), although that's a good idea, but I have learned to position it by feel. I also have a regular buddy (my son) who does a double check before descending.
To make the strap, I thieved some 1" webbing and quick release buckles from an old backpack that was at hand. That release is positioed under my chin, and or course is adjustable.
The other ends of the straps were fitted with snaps I bought dirt cheap at Home Depot along with the tool to set them. These ends are looped around each side of the headstrap and snapped each to itself. So far ~ 60 dives, boat and shore, several in strong current, and never a hint of losing it.
If you wear a snorkle, it can get in the way if you are not careful, but it is easy to position it so it does not flop in front of the camera once you are aware you need to.
Bubbles are only an issue when you are vertical. So don't be vertical when you want to capture something
YMMV