Some feel that the maximum charging rate will decrease battery life, but with the logic in the car and the liquid cooling, if any, it's not huge.
The limitations are more for if the device is on a shared circuit to prevent you from overloading it. Say you were using the included 120-vac EVSE and plugging it into the garage. That circuit might be the same one that supplies the lights and maybe garage door opener. Things might be fine until you tried to open or close the door...so, BMW gives you a way to lower the maximum draw of the car so you don't pop the breaker. On a dedicated circuit, usually, your best bet is to let the car decide, so choose maximum. It will throttle down if the battery is too hot or even too cold as required to maximize the life. Life's too short to sweat the small stuff.
2011 535i x-drive GT, 2014 i3 BEV
Soon (hopefully!) A 2021 X5 45e will replace the above