Baton Pass is perhaps one of the best moves in the whole game. Technically, if you raise a stat, you will pass it to another Pokemon, which can really define the whole battle.
For example, I used Swords Dance with my Scizor, and Vaporeon uses Scald against me. Fuck! I get burned, meaning that my attack will be halved. Well, I keep using Swords Dance until I can't raise my Attack anymore, and then use Baton Pass. I choose Arcanine, and there you go, you get an Arcanine with 6+ attack and no Burn. Your opponent is pretty fucked!
While not a mandatory move, I strongly recommend it, especially with Pokemons like Vaporeon with Acid Armor and Substitute (you can also transfer the Substitute), Scizor with Agility and Swords Dance, Smeargle with Moody ability, and pretty much everything you want (Focus Sash is mandatory in him thanks to his horribly defenses), but I strongly recommend Shell Smash, Ninjask with Speed Boost and Swords Dance, Togekiss with Nasty Plot
Pretty useful move, don't you think?