It does keep a dirt out of the tube, if it's in the frame. Think about it. The air has to get into the tank as fuel is sucked out. If that tube gets clogged, the fuel pump can slowly suck your gas tank till it collapses to a smaller shape.
Every year after that had a vapor recovery canister. This is why I try not to top off my 70 tank unless I'm on the highway and will use it right away. I don't want any expanding gas dumping out of my tube or past the cap, onto my paint.