I've talked to you about this before, and I still think the same way. I like having one customer for $60,000 in a year instead of 200 jobs for $300. Making one estimate or 200? One bill or 200? Giving directions to the job once or 200 times? The little things, too, like giving a fruitbasket to a customer is only feasible with a smaller number of clients.
Potential problems:
1. Losing a huge chunk of your revenue if one customer moves away.
2. Finding jobs like that again.
3. Pressure to please a particular client.
4. Elevated stress levels.
5. You get sick of the same place.
6. Your business begins to tailor itself to circumstances that may not exist on other jobsites (i.e. purchasing specialized equipment that you only use there).
It's an issue of what your business plan is. Not everyone can have large clients, obviously, so it depends on the market. Your personality may not work with this business model either - it's a matter of taste, and I like the flavor of a few large customers over many smaller clients.
Nickrosis