If you skim the foam, then you're more likely to be watching the pot when it comes to a boil and thus less likely to have a boilover. If you're prone to getting easily distracted by shiny objects, then skimming gives you something to do.
I think it's one of those things that gives you a greater margin of error later on, so it doesn't do any harm. I started doing it because of the similarity in making stocks.
As with any process in brewing, if you get good results without doing it, then don't worry about it. Nobody said everyone has to brew the same way. Well, if they did, they're wrong.