Its 80% of the breaker that you charge at, for continuous charging. 80% of 40 is 32 (so you need a 40 amp breaker to charge at 32). 32 amps is also as fast as the current mobile connectors (since at least 2018) charge at, no matter what you plug them into.
To charge at 48 amps ( the fastest the LR / Performance model 3s will charge), you need a 60 amp breaker (because 80% of 60amps is 48).
If you had a wall connector, and a 50 amp connection, you could charge at 40amps (because 80% of 50amps is 40). People always talk about putting in 14-50 outlets, with 50 amp breakers, but there isnt any benefit to that combination for anyone using the mobile connector the car comes with, no matter which model 3 you have.
It just allows for easy expansion if you buy a wall connector later, or get some other charging solution that can take advantage of 40amp charging on a 50 amp breaker.
