The benefits of High Command are the same as in S1914.
You get access to the Build Queue.
You can change how your units respond to enemy units, e.g. Aggressive response, Fire is fired upon, hold fire or fire if not executing another command. This is the Fire Control feature.
I am sure there are others that I use that I forget about, but I love it because of the build queue. You can set it to continue to build improvements and units as resources allow.
