Originally Posted by Fat Little Green Yoda
Wood Hammer's recoil will break the Sash, despite how much it does to Kyogre. I guess the Sash can come in handy if you aren't going up against something you'd Wood Hammer.
. A sash is nearly worthless against a Kyogre. Unless Kyogre gets a crit or something, it has no chance of OHKOing you. Several of Kyogre's usual partners have priority attacks as well which can chip away the sash anyways.
Wood hammer is pretty much ONLY for Kyogre. Blizzard takes care of Groudon, albeit slightly less effectively than grass knot, but Groudon is slower and not as big of an issue as a Kyogre anyways. You lose a bit of damage on things like Palkia, since you either blizzard them or break your sash, but some people consider Kyogre a threat big enough to warrant using wood hammer. It also helps versus Blissey, not that she's that common.
And yeah, I'd consider sitrus as well, although it's by no means mandatory. Sash helps with crap like Palkia flamethrower, while sitrus gives you extra health versus things that can't OHKO you like opposing Abomasnows.