What the hold-over arrows on icons in Finder do?
It just changes pages on the icon preview for multi-page documents.

Not spectacularly useful with small icons like that, but if you have huge icons set or are in column or cover-flow view, it's a quick way to see what's actually in the document without opening them. 

If you click away from the icon, it goes back to the first page, so it doesn't actually change anything.