Tons of things, of course!
One of the best perks of having parties is that you sell more of some specific food categories at each party which means making more profit! You can check which categories sell more on the party popup.
Another good one is collecting surprise gifts in bubbles appearing on screen while you are having a party. The gifts range from dishes to game units such as cash, spin tokens, drops, etc.
While a party is on, the tips you collect are more important than normal ones because you can make tip combos if you collect them fast enough!
And last but not the least; you get Sticker Packs! They are essential when leveling up your parties.
Be it for profit or just for fun, parties are great in Cafeland!