When it comes to downsides, the little part of your job that isn't made of stress is made of physical danger instead. First and foremost, you're walking around carrying plates all day. This may seem insignificant, but over time the pressure and pain will build. It puts a lot of wear and tear on your body, so you should consider a good yoga routine or warm-up before you start.
You'll also be walking around wet and greasy areas, so slips and falls are an ever-present danger. The restaurant will probably require you to wear slip-resistant shoes in order to lessen the chances (and their liability)—and even if they don't, we'd highly recommend it.
You can't really serve food if you've broken your leg, and there's no such thing as paid sick leave in the restaurant industry.
In fact, if you aren't careful, anything and everything could turn your shift sideways. Arm and shoulder strains from carrying heavy loads of food and dishes are fairly common.
Occasionally you may get burned, either from hot plates or by bumping up against a hot appliance in the kitchen. Foodborne pathogens are aplenty on uncooked food, and you'll be dealing with plates that people just got done drooling over, so make sure to wash your hands.
And let's not forget all the cutlery you'll be handling—emphasis on the cut. Is this the best time to remind you that you'll likely be running on little-to-no sleep? For the sake of everyone around you, please just try to stay focused. We realize that's asking a lot.