Geography and creative stop being separate decisions
Splitting campaigns by county only helps if the message changes with them. A Hamilton County ad and a south side ad selling the same job should not read the same, and usually the same person needs to own both.
When targeting sits with an ads freelancer and copy sits with somebody else, the split gets made and the messaging never follows, which delivers most of the extra complexity and none of the gain.
The website becomes part of the campaign
Multi-county programs need pages that speak to each county. That is website work, and if the developer is a separate vendor with a queue, the pages arrive a quarter late or never.
One team writes the campaign and the page together, which is why the setup takes weeks here rather than months.
B2B and consumer campaigns stop competing for the same budget
This metro has a large logistics, distribution, and life sciences base alongside its consumer economy. Plenty of local businesses sell into both and run them out of one undifferentiated account.
They need separate campaigns, separate landing pages, and separate reporting, because a warehouse operator and a homeowner arrive through completely different journeys.