I think he was referring to those instances where you have something which as far as you can tell at the moment should be a certain height but inexplicably (at the moment, because you need it fixed now!) has this weird margin underneath it. With a quick look at the web inspector and your code you can't work out where it's coming from so in the interests of fixing a problem now, you might `overflow-y:hidden` it with the intent to come back later.