You probably don't need it. The server will adjust the difficulty to suit your ASIC miner.

If your ASIC miner isn't able to function properly because the work it is getting is too low difficulty at the beginning when it connects, then you can set a higher minimum as a work around. This should not happen to anyone, and you should let me know if it does.

If your internet connection has extremely low bandwidth then you may want to set a high difficulty to reduce data traffic to an absolute minimum. This may be useful if anyone is still connecting with an ancient 56K modem (as used in the 90s) somewhere in the world. Not sure if this actually happens in real life.

Or maybe you are renting miners and the rental service requires an extremely high difficulty. Setting the necessary minimum should work. In some cases I may also be able to add logic to automatically detect the rentral service and set the proper difficulty automatically.