OP
My point was, why dive to 100' to see nothing, when you can see nothing at 20'. Why bother going that deep?
There are a few reasons to want to dive to 100', even to see nothing. The most understandable reason, I suppose, is training. I can only afford to go on so many boats in a year, but to keep my skills from rusting away to nothing, I need to get more bottom time than that. As when I do go on those boats, it is frequently to dive wrecks that are a long way down, I like to keep in practice. My less understandable reason is, I like it. It's a very different feeling, 100' below the surface. Perhaps I'm a bit strange, but I like it (I don't mean being narced, although it certainly adds to the experience )