CMD isn’t really a tool used for remote hacking as such, however once you’ve gained access to a box you’re 99% of the time going to be doing everything through a command line. You’ll be doing stuff like ensuring persistent access to the machine (eg. I read somewhere that one guy used ‘schtasks’ to set up a reverse shell back to his attack server). Also you’ll be nabbing loads of info about the network and all the users running on the box and covering up any noise you made in the process. So CMD is important AFTER you’ve done all your hacky-magic stuffs and does play a role in hacking.
You should check out this index of all the different commands on Windows CMD and play around with them and some scripting to see what you can really do with it: http://ss64.com/nt/