If you gather poisonous mushrooms, there's a chance these are served to customers and they won't pay for their order and complain "they'll get sick".

As for the purpose of the restaurant view, I just found it funny.

Upgrades explained:

• More staff: Counter space is increased so larger area where customers can get their order.
• Increase mushroom yield: Each upgrade increases the number of mushrooms you get from each mushroom gathered.
• More mushrooms: Spawns more clickable mushrooms.