Cherrim's only use is in Double Battles/Triple Battles, where it pairs well with a Pokemon such as Groudon. While it does nothing itself, it makes your ally very powerful in the Sun. Even then, I consider it to be a worse teamate than something like a Whimsicott, who can set up Tailwind and Light Screen for you while also weakening the foe with Memento, which gives you time to set up a boost move. In Single Battles, Cherrim is useless.