Aym is a character you can meet near the second entrance when you've just arrived via the Interceptor.
You can ask him about the opened gates near him.
He will say you that those opened ones lead to areas you've already been to and you secured them. You can go to complete a few things in there for brouzoufs. There are enemies in there, for sure - because the Federation is trying to secure those places, the Looters are trying to scavenge any valuables and there can also be Meta-streumonic creatures, as those are in habit to appear anywhere.
Note: The least dangerous (mostly abandoned) area is the Forgotten Center, there can be few Manducos near the entrance and few Looters in the area. Jians can be also operating there in small numbers, but that's rare (watch out, they can be hostile because of their unstable relationships with Culter Dei - the truce applies only in the Temple HQ). Most of the area is abandoned. You can meet some Culters operating in there as well.