TLDR: That's fine as long as there's no current
...flowing through the circuit when you flip it. Interrupting EV current would be bad for the breaker. Some breakers are listed to interrupt current, but a 2-pole 30A won't be one of them.
Be VERY careful with EV ampacity
It is not important to have a Super Fast EV charger. This is an EV myth. Even a 240V/15A circuit is good enough, when backed up with DC fast charging for rare exceptions that 90 miles per 12 hours is not good enough.
What is important is not burning your house down.
To start with, charging must be sized for the available amps in the service. That is decided by a NEC Article 220 Load Calculation, not "some other method lol".
Next, Codes need to be followed. The socket size needs to match the breaker size. A 30A breaker with 30A wiring needs a NEMA 6-30 or 14-30 socket, not a 50A socket. Many people use the "travel unit" that was supplied with their car. Those have exchangeable dongle plugs so you can plug into any available plug. They make a wide variety of dongle plugs. It's extra important for socket to match breaker because the dongle plug tells the car the safe amps it can draw based on the socket size! By improperly using a 14-50 socket with a 30A wire/breaker, you told the car "you are on a 40A or 50A circuit".
The travel unit, being a travel unit, comes with included dongle plugs for the 2 sockets most often seen when traveling: the common one, and the large RV plug NEMA 14-50 found at every RV campsite. Because it's for travel. This has confused many people. Actually, the "standard" EV socket will vary to match what your house is able to provide (NEMA 6-15, 6-20, 6-30 or 6-50/14-50) and EVs don't use neutral so a 4-wire socket is wasted. You can buy a wide variety of dongle plugs; they're not expensive and they will tell the car the correct charge rate.
So I say, emphatically - clean up your act and get legal. This is nothing to fool around with. You seem fastidious and want things in a certain order/way, wanting to turn a breaker off to save 2 watts - I think you have a whole lot more important stuff you need to fix first.
After doing a Load Calculation, either change the receptacle and breaker to one appropriate for your available power, or if 40A is available, rewire the circuit with 40A wire and breaker. (the travel EVSE assumes a NEMA 14-50 is a 40A circuit because that socket is used in 40A circuits, since 40A sockets are not made). On travel units, use an approved dongle plug since it has the microchip which advertises the available amps.
Note that per Code and UL standards, EVs actually charge at 80% of the breaker/socket/circuit amp limit. So an EVSE that thinks it's on a 40A circuit will tell the car to charge at 32A. That is probably what you have been doing. Breakers have some slack, or you may have a defective breaker (Zinsco, FPE, Challenger).
Use EV's ability to electronically stop load.
You may have noticed when you interrupt large 20A+ loads, there is a GIANT BLUE ARC that jumps across the plug as you disconnect it. This is mildly bad as it creates arc damage on the connector or switch.
You may also notice that if your car is charging and you push the button and pull the charging socket out of the car, NO BLUE ARC. Why is that? Because when you push the button, the car knows it, and immediately suspends charge electronically so by the time you pull it out, 0 amps is going across it.
This is not your father's battery charging tech.
The car will also suspend charge electronically if you tell it to stop charging in its console or at the EVSE. (the EVSE will remove the "authorized to draw power" signal, and the car will stop charging.)
So one should never use a circuit breaker to do a hard cut of charging power, unless there is a problem. Use whatever connectivity options your car or EVSE provide and tell it to suspend charging.
If the EVSE is definitely unplugged and not drawing, I don't see a problem cutting at the breaker, but they have limited cycles. Except.
Getting breakers rated for that, though.
The big blue arc will wear out breakers just like any other switching equipment. Normal breakers are not rated for this duty.
However, they make breakers which are, called "SWD" or Switching Duty". In commercial or industrial spaces (e.g. CostCo) they often control the lights directly at the circuit breakers and don't bother having normal switches. They use special SWD breakers for this duty. This is on lighting circuits ranging from 15 to 30 amps, single-phase 1-pole.
When UL found the manufacturing cost difference in SWD vs non-SWD breakers is negligible, they mandated all 15-30A single-pole breakers be SWD.
That rule does not apply to 2-pole breakers because they're not used for lighting.
"Hey. I'm aware of a product called a handle-tie that can tie two single breakers together to make a double. Can I grab two 1-pole 30A's that are SWD, and tie them to feed a 240V EVSE?" Not with a NEMA 14- socket, because that has neutral, and with neutral involved a problem on one pole needs to trip both -- common trip. Handle-ties do not provide that (really), it only comes from factory made 2-pole breakers via an internal mechanism. (European DIN rail breakers can field-install that mechanism). If you change to a NEMA 6-xx socket which does not have neutral, then you can use two SWD breakers with a handle tie.
