Why Use Zones And The Smart Thermostat?

Having tried to read up on zones and the features of Tado, its my understand that there are a lot of overlapping features to try and cover a number of potentially scenarios but I’m struggling to work out which one best suits me.

I have a smart thermostat when I bought the starter kit. We were having work done on the house so the new boiler needed a thermostat. This is located in the hall and is assigned as the zone controller and I have since accumulated smart radiator thermostats for most of my radiators.

Downstairs smart radiator thermostats: kitchen/ diner, living room and hall.

Uptairs smart radiator thermostats: Bedrooms 1, 2 and 3.

Dumb thermostats: downstairs utility, upstairs bathroom.

My current setup is that the smart thermostat is assigned as the zone controller and each smart radiator thermostat is independent and will call here where required. As I have so many smart radiator thermostats in the important areas that can call heat does it not leave the smart thermostat in the hall redundant because its not controlling the heating of the main areas and is it therefore ok that I set that to a constantly low temperature so that it doesn’t interfere with the rest of my setup?

Would it be beneficial for me to set up zones for say downstairs and upstairs and if I did set up a zone, what benefit would that give me as the smart radiator thermostats can call heat independently (which helps due to say bedroom temperature variations)?

If I were to set up a zone, how would I determine which is the best smart radiator thermostat to choose as the zone controller?