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In the USA, you have two settings to limit the charging rate...one when it is using 120vac and a second one when using 240vac.
The only reason BMW allows you to set the charging rate lower than maximum, is that the device might be on a shared circuit, and pulling its maximum might cause the protection circuits in your home to trip. It could be useful if you have a solar cell system, and you don't want to use grid power, so you'd limit the maximum.
You cannot damage your EVSE or the vehicle with correctly working devices on both ends.
The EVSE shouldn't be plugged into wiring (or hardwired) that cannot handle its maximum output safely. Assuming that's true, when the EVSE sends out its pilot signal, that indicated to the vehicle how much power it is ALLOWED to use. THen, the vehicle will pull what it wants never exceeding what it was told was available, or was told via the iDrive menu up to that. It's a pretty foolproof system.
So, the only reason to drop the maximum in iDrive is if that would cause the EVSE on a shared circuit to overload things. In the US, say in your garage, you may have it plugged in, and that same circuit might power your garage door opener, or you are using some power tools. Then, you may want to tell the vehicle to not pull max out of the thing, otherwise, you might pop the breaker.
Fuses and circuit breakers (at least in the USA) are there to protect the wiring, not the device specifically. On a device that has an internal fuse, that is different, and that is trying to protect the device from overload. WIth a working device, you can't overload an EVSE, or damage the vehicle.
Maybe another good example is to consider your vehicle as a smart device...you can plug a 50w lamp into a circuit that could handle a couple of thousand watts...nothing bad happens. If you were to try to plug a space heater that would try to draw 2000W on one capable of 1500W, you'd pop its breaker. In the case of the EVSE, and the vehicle, they're smarter, and the vehicle can adjust itself to never draw more that the EVSE says it has, or up to whatever you've told it to pull.
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