Pros/Cons of Differing Population Sizes?

[Brian Kraft]

Would you smartypants (with "bigpockets") please weigh in and innumerate the pros and cons of investing in markets of varying sizes? A commonly stated risk of a smaller population is possibly having an employer, that's providing jobs to a rather large segment of the population, leave/shut down. 

What are other things to consider (I know there are many!)? How does your strategy play into your decision of location as it relates to population size?