I was just reading an article about the "importance" of a thermal
expansion tank to extend the lifetime of water heaters, T&P release
valves, hot water fixtures, etc.

On the other hand, we have never had one in our house or where I grew
up and I haven't "noticed" any problems.

Specifically, we have a 40 gallon gas-fired water heater on city water
with 3/4" inlet and outlet to the water heater and copper plumbing
throughout the house. We have 4 bathrooms and a kitchen. The city
water pressure comes in at about 85 PSI.

How important is it to add a thermal expansion tank or is this one of
those "if it ain't broke, don't fix it" kind of things?

Alternatively, is there enough "give" either forward through the hot
water plumbing or backward through the cold water plumbing (and
ultimately maybe even back into the city mains) to allow sufficient
room for expansion?

If a thermal expansion tank is recommended, any suggestions on brands,
models and sizes?