With any competently designed battery management system, a lithium-ion battery will have some sort of reserve even if it specially won't use it for its main purpose. I've heard claims that most lithium-ion battery systems could be extended to about double the capacity (increasing the voltage range) if users would be OK with considerably fewer overall use cycles.
My portable devices will shut down at a certain point, but the battery is still providing power where it will display an empty battery symbol if I press the power button. I've heard of EVs refusing to move at a certain point, but the battery management system is still providing low-voltage power to the onboard systems.
yup - Its always been the case that that the deeper the DOD, the harder it is on the battery.
The BMS is there a a bumper stop, but Ive never seen a case where shallower cycling doesn't contribute to longer life.
The ICE version of the "drive it till its out of fuel" game is when you suck up all the crud sloshing around on the very bottom of a tank or burn out the fuel pump trying to keep starting it when it depends on the fuel to keep cool.