I think it provides environment.
TL;DR: It provides a dynamic battlefield that Zeus can make use of (which is good and bad as it can help and/or get in the way). It provides support structures (CAS, Transport, Arty) on call. It provides AI to populate buildings in a town/city/military base and you don't know where they are. Provides civilians that 'do stuff'.
In my test mission, I have blufor moving to their objectives and opfor moving in the opposite direction. I have a bunch of rebels/insurgents holding the middle, being backed up by the opfor force moving south (from the north) which bluefor is trying to take that center section away.
Then I have a squad of 'playables' and their objective is ... whatever they want.
In one instance, I switched to Zeus and created an objective for them to take a town on the right edge of the map. I exited Zeus and had my AI team use the Alive support resources insert them into the hills S of the objective. We moved in to the town through the valley and cleared it from an Alive controlled occupation force (AI roaming force and AI populated buildings (random based on frequency settings) with civilians in the town. Then we extracted via the Alive support assets. The benefit here is Alive provided the support helo insertion and extraction, the unknown AI threat and the civilians. Zeus could have augmented that as necessary.
In a second instance, I switched to Zeus and created an objective in the center of the map - to take and defend a town. Using the Alive Support we inserted by helicopter into the hills to the east of the objective and proceeded to push into town. Blue forces pulled into the the objective from the east (they didn't know it was an objective other than Alive gave them one that happened to be in the same area as the player/zeus objective). Opfor entered from the NW. Things got really chaotic (which might be a minus) as AI fought AI and the player squad. I took some casualties and called for CAS (Helo) and extraction, had to pop smoke for the Alive support extraction helo to land and pull us out. I could have called in Alive artillery but no one would stay still...
In the first instance, because it was off to the side of the action, it was relatively controllable. In the second, I had no idea what was going to show up on either side and I ended up in the middle of a big fight.
I'm not sure it will add to what we are looking to do (I'm not sure what we are looking to do) or even be beneficial. For small, 20-30 minute missions, probably it only adds support. But it has the capability to add more for longer campaigns.