Reservation needed for all restaurants?

Hello everybody,
I am flying to Japan next Monday and I never thought about reserving restaurants far in advance until I read this forum... Is it always necessary?
I am probably going to try local food in izakayas and medium-priced restaurants.
I am pretty sure I am not going to any expensive / Kaiseki restaurants due to budget reasons.

How early should I make a reservation for a table in a ''normal'' restaurant?
Any advice could be very helpful.
Thank you very much in advance.

Reservations are generally not necessary unless you want to dine at a particular, popular restaurant.

I have been to Japan many times and never made a reservation. Don't worry!

I am a Japanese, and this is just my feeling about reservation in the dining place in Japan.

Reservation necessary: some very famous and popular restaurants (like with Michelin stars): less than 0.1%.

Reservation recommended: Some expensive restaurants (like in the fancy hotel) or you are big group: 1%.

Reservation possible but most people do not: Middle class restaurants (less than 5000 yen per person for dinner): 20%.

Reservation impossible: People just go into the restaurant and order something. Note that some popular restaurants do not accept reservation: The rest.

If you would like to have fine dinner (Japanese style or other styles), you might better reserve your seats. However, if you would like to enjoy local foods, do not worry.

Enjoy your dinning in Japan!

If you want to eat in a particular restaurant at a particular time, reservations are always recommended. If you want to eat dinner in Tokyo on a Friday night, reservations are essential. Even if the restaurant turns out not to be full, you'll get a better table if you reserve.

How early should I make a reservation for a table in a ''normal'' restaurant?

A day or two ahead of time is usually sufficient, unless it's a Friday evening in Tokyo, in which case maybe a little further in advance.