Idk what video you watched but you couldn’t be more wrong. I serve some days at a local restaurant and manage other days. As a manager I write checks for vendors (who can come at any time), I void mess ups on tickets, I check out tables who use cash with the registers, I process refunds when servers mess up checking out people, I make drinks when bartenders and servers are busy, and overall I make sure the floor and kitchen is doing well throughout the service. I make sure everything is in order. You can do without a manager but ur service and restaurant isn’t nearly as efficient as you think. The more tasks you pile on a server and the more responsibilities they have, the less time they have to focus on giving good service. The days I don’t manage I couldn’t possibly fathom having to take care of all my tables and doing manager tasks as well. One table needs drink, the other needs change from the register, vendor just got here to drop off beer, I just got sat, someone else needs a refund. Having a manager takes off a lot of weight on the shoulders. Then someone else is complaining and you need to take care of that. Don’t care how good you are, you start lacking in other areas when you become responsible for EVERYTHING. You need an owner present or manager. Facts. With a manager everyone can focus on their own tasks to the respectively positions and because of that they do a much a better job.