Out of curiosity, how large of a grid is "sprawling" and how small of a grid is "too small"?
Depends on what you are doing. I'm super conservative on this idea. I need to think like someone who's not me. 
I'd say, no more than 1 room per nieghborhood. But, let's say this:
Neighborhoods - Little Asia, Little Europe, The Upscale Brownstones, City & Corporate District, The Nightlife District, The University District.
Suburbs around Night City - The Pacifica Playground, The North Oak Military Suburb, The Rancho Coronado Beaverville, The Heywood Industrial Zone, South Night City, Westbrook.
Misc: The Badlands
That's 13 rooms that should be if you were trying to build a thematic space.
For the Neighborhood and Suburb descriptions it's super easy to just use the descriptions from the book. Or at least use those as inspiration. Descs more or less done.
You could branch out each of the neighborhoods into a few extra rooms since they mostly have 'multiple locations' within. Or, what's smart grid making is make 'places' out of those locations. You might be more of a traditionalist than I, but when you make places like that it keeps it easy to find people and easy to RP, but easy enough to have non-widespread locations. So, rooms/places, whatever you want to do. If you make rooms, from there you are now needing some 'hangouts'. Instead of say describing places in the places desc, you now might create exits. And then a place with 1 room is more or less a waste, so you need 2 in each place.
This is why it gets sprawling. 13 main rooms, 18 sub rooms off the 6 main areas. So, 7 main rooms that need 2 sub rooms, 18 additional sub rooms that need 2 lower rooms than that. Now you have, 36+14+7+6, 63 rooms.
Say you launch with a really good player base for today. We'll say 8 regulars. That's 2 groups of 4, more likely 2 groups of 3 and 1 group of 2. So, you have 3 groups taking up 3 rooms out of 63 places you built. That's sprawling to me, but it might be acceptable to others and you. Especially since about 13 of those rooms are already 'made-ish' for you from the descriptions.
Two options to shrink that:
So, you can trick the base. If you cinch it up to where people are only playing in the bigger rooms with a few hotspots with locations. So you do a City & Corporate District room. In that room you put a line item describing what areas exist within it. Corp Center, City Center, Bank Block, Med Center. And you pick 2 of those places to create hot spots. Now you have just 13 main rooms, with descriptions that cover the bigger areas. 2 spaces each, that's 39. You are getting there. 3 out of 39 still seems like a lot of wasted space but at least it is only 39 rooms instead of 63. And I'm not even considering OOC areas or chargen areas (depending on how you build out Chargen).
I'm always thinking of 'How do you get players together, make it easy to find one another, not get lost, and still have rooms that speak to theme?'. For me, it'd be enough to have the Neighborhoods (6 rooms), plus the other areas (7 other main areas), and maybe to give more theme, the 18 sub-areas off the neighborhoods. And let people just invent the location they are at in specific. Which diner/which place/etc. Just emote it. That gets your work lowered to 31 rooms. The bigger trick here is that you only really are coming up with base descriptions that are mostly in the book already. Laying the groundwork for people to have theme. So most of your work is done. And the creativity piece comes in from the players.
To me, that's enough to launch with. And then after a while, put out a request for place-descriptions or hotspot ideas. "Where have you been RPing the most? What diner? What location? What's it look like? How do you describe it in your plots?" Etc. And take that work and make them places the players decided instead of you created and no one used.
Talk about sprawling. I'll stop here. Your choice. Of course, the top way is still far smaller than most places start with. But we don't need a map to play, we need a system of dice rolling, character sheets and a place to emit. All that's in theme with the system. You can grow it out as you get people and you need to support more than 1 group RPing in a particular sub-room at once. Ya know? I said I was going to stop, so now I will for realsies.