What’s the intent? Spare parts? Saving time reloading at the range? Carrying more ammo on you?
Magazine fed autoloaders are pretty miserable to reload if you don’t have spare magazines. Magazine break and wear out.
For carry, there are some malfunctions that are best fixed by swapping mags, besides being able to carry an extra mag for reloading.
I shoot a pistol match where I need to be able to shoot 30 rounds without taking the time to reload mags.
Different use cases call for different correct answers to ‘how many is enough’.