The appropriate dress code for an employee in a restaurant really depends on the restaurant. The type of dining experience the restaurant wants should dictate the dress code. For example, a casual restaurant will have a different dress code than a fine dining establishment. The fine dining restaurant probably requires jackets and ties, while a casual restaurant might require t-shirts and jeans.
Uniforms are important because they create an atmosphere and clearly show who is an employee.
[What] employees wear is highly important, especially the host and bartender because they’re the first people guests interact with. They set the tone and create a first impression with guests. (fsrrmagainze.com)
Another important aspect of restaurants is that the uniforms need to be clean and neat. Neatness reflects hygiene and the restaurant’s cleanliness, and a restaurant had better be neat and clean!