@jamesf123 It really depends on what your priorities are.
I have been in CH for 10 years out of which 8 were without a car, I also had a GA for some years (as a SBB Employee).
If you live in a city e.g. like Zurich you probably dont
need a car for your everyday life.
However it does help in many circumstances e.g. you can go skiing with the train, done it several times, but for me going there with my car is 5x easier since you can just load your skis and stuff in the car and not worry / pack light. Also some day trips, hiking routes etc. are easier to reach or cheaper to do by car, especially if you travel with 4 friends (so 4 people would have paid tickets).
In general however if you make your decision based on money/expenses then of course it is way cheaper to have a mobility abo or rent a car when you need one. For me owning a car gives me a feeling of freedom (i am not sure if this is the correct formulation, i am not a native english speaker). Freedom aside I use the public transport or my bicycle to commute to the office since moving around with the car in zurich is not very efficient time-wise.