It is just something I am interested in being able to do. Maybe it is a milder form of Body Integrity Identity Disorder? I have been through a lot of physical pain, so I am not really thinking about that as a part of it (though I know a lot of piercers do). I want the results, which is to be able to move both halves individually.
As far as tattoos, I like art hung on walls or put on other people. Or maybe I should elaborate further so that the whole tongue splitting thing makes more sense.
This first picture is of henna, but it is actually something I would consider having as permanent ink (maybe not in the same place, but a similar design). In my mind it enhances the hand. It highlights what is already there and makes it more accentuated. At the very least, it does not detract from the body at all. It is very obviously on the body, almost one with the body. Like the stripes naturally are a part of a tiger's skin and fur.
This second one is simply placed on the body. It doesn't show off his arm, it covers his arm. There is a reason that when people have tattoos covering their whole arms they are called sleeves. It is so completely covered that it looks clothed. While I admire and love to look at these on other people, the look simply isn't for me personally. I enjoy my body actually looking unclothed when I am not wearing clothes.
Edit: And as for the risks, I will take my chances. Call it an unnecessary risk if you want, but it is one of those things that I don't want to regret not doing.