I think the gates are just that.
If you build an outpost down on a barren planet, and everyone had access to a fleet or SRV's, they would be driving between all the buildings, potentially running over equipment.
The gate give an exit and entry point, keeping the disruption from SRV's in the compound limited without building walls around it. It's also a place to put a name board - did someone say they read Delta S-2 on a gate somewhere?
Delta S-2 yeah. I believe it was AvvieXB1 our delta site finder.