Some companies have strict rules about making their employees wear a uniform all the time in the workplace.
In my opinion, the reason for that is related to the job type, for example, in jobs related to meeting customers like customer service or sales in shops or supermarkets they should wear a uniform to make it clear that they belong to the staff and customers can find them easily to get help, also in banks, tellers, customer service and all other jobs there that related to meeting customers they should wear a uniform mostly a suit and the colour can vary from a place to another.
Moreover, some big companies also ask their employees to wear a formal uniform to keep the company image good in front of their clients, some other jobs make it clear the hierarchy inside the organization for example the doctors in the hospitals wear white coats and nurses mostly light blue or pink so patients can identify them quickly, other jobs the staff my dealing with chemicals or harming things so they are wearing the uniform to protect them and their clothes from dirt and chemicals.
Another example is in restaurants the waiters should wear a uniform to make it easy for the customers to recognize them easily, and also inside the kitchen the cooking team and the chef wearing hats and coats for clean and hygiene reasons.
To sum up, uniforms are necessary for certain types of jobs for several reasons, such as to make people recognize the staff easily, or for hygiene and safety and sometimes the place itself requires their employees just to wear formal clothes all the time as important meetings are a key part of their job type.