There are reasons for this that go beyond just convenience or protecting wire sized circuits downstream. You may not have had, or desired to do so, but that's the reason for the "requirement" (or maybe custom or maybe recommendation).

If you were messing in your electrical panel and a screwdriver got welded across the 50 amp breaker, for example you'd disconnect the battery switch. Unless you needed the electrical panel "hot" for some reason, you would have been best advised to use the battery (shut-off) switch to make sure something unexpected or unwanted happens.

We have fuses that never (or hopefully) never get blown. Take the old, big, cartridge fuses main-service fuses in your house. They are there for a reason. I bet less than 1/100,000 ever get called-upon to make the ultimate sacrifice ;^))).

I was warned when jumping a solenoid with a screwdriver that a mistake would lead to a welding the screwdriver accross the connection and could cause a fire before I had a chance to disconnect the battery. Our engine battery cuttoff switch is about 3' back and just below where my knees are from the solenoid to the starter. I was warned that it would be a mess, even if I was very quick to shut-off the battery. Clearly, he said, if the screwdriver can't immediately be pulled-off -- CUT THE POWER by the switch.