For me the cost of the consumables (i.e. shaving soap and blades) for DE shaving are just so cheap I might as well shave every day. If I run out of aftershave I can always use my alum block.
Of course there is the feeling that I'm respecting myself by shaving every day.
Then again if I accidentally nick myself badly (which hasn't happened for a while now) I'll stop shaving for a few days to let it heal. But that's a different story.