I don't know how true it is, but years ago I heard about a dude getting his dick bitten off from 'road head' and having an accident.
Just doesn't seem worth it to me.....at all.
Then again, I'm boring and old fashioned. I prefer to get it while I'm relaxed (see: not standing) and not laying too flat, because when I'm IRON, rock hard I don't 'bend' really well towards my feet, if you know what I mean.