The AI can't handle substitute in a lot of games. If your opponent has thunder wave or wisp, they will often continue using it until your Pokemon is paralyzed or burned. So even a mediocre Pokemon like Audino can sweep BW1 Shauntal for example, by setting up substitute and using work up + shadow ball. Substitute is also nice for dealing with stat lowering moves, like bulldoze. The AI often uses bulldoze or rock tomb until your Pokemon is slower, completely disregarding the type chart in the meanwhile. If you set up a sub against BW1 Marshal with Serperior, it will just keep spamming bulldoze against your sub, giving you ample time to set up with coil and sweep. So many boss fights across the series can be cheesed like this thanks to substitute, it's really dumb. Sometimes I even consider banning substitute for myself because it just feels unfair.