Can you save ps2 games in a usb drive instead of a memory card?

If you mean, can you save, while playing a game, to flash drive instead of memory card, then the answer is NO. A PS2 game will always look for a memory card, usually in slot 1. You could always buy just 1 card, then use AR MAX or Codebreaker to transfer all the saves to flash drive for storage purposes. But you would need to transfer a save back to memory card if you wanted to play a saved game again.

Then what is is used for?!