If you're AFK, you're not playing, just wasting a slot. There is no point in being AFK as far as the games structure or function are concerned. You can't sell stuff directly from your character, there's no achievements for not doing anything, and no one really cares what you look like.
There's no practical use beyond the fear of 1017 when they try to get back in, which is ironically fueled by the very people who AFK.