Articalys said:
See, this is part of the metagame strategy I don't understand -- wouldn't the substitute get broken in the same turn it was sent out if your opponent attacked you?
Just to comment further, Substitute can be valuable in many situations. If you predict that your opponent is switching to something to counter your Pokemon, putting up a Substitute is a great check to what they're bringing in.
For instance, you bring in your Hydreigon after a Pokemon faints against their Espeon. They switch to their Scarf Jirachi (who vastly outspeeds you) to take the incoming Dragon attack, but you use Substitute. Now behind your Substitute, you're free to pick Fire Blast and eliminate Jirachi.
Even more than that, you can setup a Substitute in the face of status as well. Trying to statup with your Haxorus, and you're worried about the Spiritomb burning you? Just through up a Substitute and the move fails.
Aside from that, it helps with luck too. If a critical hit lands on your Substitute after you've secured 6 Curses and 3 Amensia's with your Registeel, it doesn't matter. But if it lands on him without a Substitute, it will cut through those boost and probably KO him.
That's critical in Battle Tower/Subway as well. Criticals are everywhere, and trying to lessen the 'chance' helps.
Hope these are some good examples.