I have a Tesla and haven't had occasion to use a non-Tesla L3 charger, but my understanding is that different networks may make it easier to pay without a credit card, or offer discounts for being part of their network, or maybe don't have a credit card reader at all? And having their app installed on your phone (or whatever) will make it easier to find them or view the realtime status.

So I would think it's simply easier to always use the same network or else you're juggling apps and payment methods.