What exactly does the prefix "за-" do to a verb? There are probably hundreds of verbs that can take that prefix. Do they have anything in common? Please give a few examples. Also, please specify if there is any difference in this respect between verbs of motion (ходить-->заходить) and other verbs (хотеть-->захотеть).
I read somewhere that in some cases, "за-" gives the verb an air of informality. How accurate is this?
Thanks in advance.