[BryanW]

I'd agree that shallow diving might seem more "casual" and might therefore lead to more risk by the diver not taking it so seriously. However, I've always found that one minute underwater feels like two or three at least, so the risk of overstaying is quite low. The SWB point is interesting. I thought that it occurs in the top 10m because that's where the partial pressure difference is greatest, but if you don't go down to any depth, there isn't so much pressure acting on the blood gases in the first place - is that right? I'm a bit sketchy on the theory.

Of course there's great value in being able to go deeper - I've been to several places where there was nothing above 15m, so if I wasn't comfortable at that depth I wouldn't have got close to anything. And if i see a turtle at the surface and it dives to 20m I want to be able to follow it comfortably. But it's heartening to know that the general freediving community's apparent fixation with depth was probably mostly in my imagination.

Cheers, Bryan