The KVM allows direct keyboard input and monitor display, as though you were at the machine, in this instance imagine if you were doing some pretty major network reconfiguration to a server, RDP/terminal services requires the network on the machine to be functional, similarly ssh access to a linux server does.

The KVM allows you to work as though you're physically there (with a couple of exceptions) so you can change bios settings, cancel that chkdsk on boot or even boot into safe mode, all of which cannot be done through terminal services/rdp.

Obviously you're not there and can't press the reset button or a power button, however there's IP connected power distribution units for that.