I think these NPCs might be useful in a few ways.
For one, staff can expand or contract a groups presence based on player population. Fewer PCs? Move some of these off to some corral disconnected from the game world. More PCs? Bring in a few more to scale the game's available business opportunities. I rarely interact with this aspect of the economy but many players have voiced concerns about the economy suffering when NPCs stopped buying things as frequently as they once did. If the flow per NPC is down, one can possibly compensate by increasing the number of NPCs to manage that flow.
Also,one could have more room to expand or contract groups based on IC events. A corp scales up security in response to recent threats? Drop some already made and ready NPCs into place. Things settle down, pull them off. A gang doing very well or poorly? Same thing! The ability for GMs to easily increase or decrease presence might help make the world feel more reactive with a low amount of effort required.
Another angle, though perhaps not the last, is rotation. I'd actually love to see this in more ways that just this but this would be a start. Maybe take some of the NPCs that have been on the streets and in the halls repping whatever group and put them off the board for a while, replaced with new faces. Then, as time goes by, rotate these static NPCs every so often to help provide more of an illusion of a changing, shifting world.
I'm sure that an expanded stable can be used in many other ways, giving GMs more tools to make little changes to the world that might help make it feel a little less static.