Reservations are a sign of respect and those who reserve get better tables. You may show up at 8 pm and find many empty tables and be turned away because they are reserved for later that evening. Since many places now take reservations on line it is less onerous to accomplish given language challenges, but online has to be done (usually) the day prior. I often called restaurants the same day about 6 pm for reservations later that night except on Saturday night.
A couple of exceptions: some pizza restaurants do not take reservations, and off season it is less critical than Spring thru Autumn and over Christmas holidays. In January on a Wednesday you can walk in almost anywhere. 😁