How crucial is it to have reservations for meals (Madrid, Granada and Barcelona)

We just got back from Barcelona and Madrid. We were surprised that we did not have reservations (we were on a RS tour) and not sure when we would be free for lunch or dinner. We got In every place we wanted. We did go very late a few times 10:30 ish for dinner and late for lunch got in before they closed , but we were surprised very different from Italy where we needed reservations everywhere.

We did eat Tapas or shared plates most places. The food was amazing. Enjoy
Do you have the RS book? We went to places suggested there or ones our hotel or guide suggested.
We also did two food tours that were great

If you have particular restaurants that you want to visit, I suggest making reservations.

If you do not, you are still sure to get in somewhere.

I always have a list of restaurants that I want to try, or return to, so I always book my dinners ahead of time.
IF you are ok with standing at the bar, or next to a ledge where you can perch your plate, you can just show up at a bar for "tapas." Some, but not all, bars take reservations for tables.

With the giant breakfasts offered by many hotels, I usually skip lunch.

One place in Granada popular with locals and tourists is LOS DIAMANTES; I believe that they now have three locations but the one I know is on Calle Navas. The earlier you go, the less of a crowd you will encounter.

Great seafood in Granada: BAR FM. https://barfm.es. Very high quality product, fairly priced but not inexpensive.

In Madrid there is a clutch of very good restaurants and bars in the Retiro district, EAST of the park. You need to book for a table, but they all have bars where you can eat and, hopefully, find a seat. This is the area I go to most often for dinners in Madrid. Most open at 8:30pm and some at 9pm. They are very popular with locals so I always book ahead. If you want some names I will give them here.

I would like some restaurant recommendations for the Ibiza/east Retiro neighborhood if I may ask.

I was there last week and I went to Triana and it was quite nice. Also went to tasquita Manuel becerra and Baldoria slightly north of there, both great.

I ask because I’ll be staying in that Ibiza neighborhood for my next trip to Madrid, thanks.

It's a really great area and easy walk north to Salamanca. I once stayed there, in an apartment; the apartment was bad but the area=great.

Here are a few of the restaurants I like there:

LA CASTELA
TABERNA LAREDO
LA CATAPA
MARISQUERIA RAFA (more formal than the others; very correct service and excellent seafood; you can also take tapas in the small bar area in front)

ARZABAL was also good but I've to been there in a long time...still gets good reviews.

Cool thanks. I actually walked by La Castela and it looked very inviting.

Let me know if you go to LA CASTELA. I'd go back next time I'm in Madrid..

Keep in mind that January 6 is a holiday in Spain. We were in Cadiz a couple of years ago at that time and found that restaurant openings can be hit or miss on the 5th and 6th. So I would definitely line up reservations for those dates or have alternate plans (we cooked in our apartment).