I don't think so, or at least I don't think that's the primary reason. I think the idea is to have people develop a breadth of experience working on different types of problems and in different countries. If you're a specialist in, say, the Middle East, it's good for your career and for State if you have experience in a variety of different countries in the region.

I think they also try to have foreign service officers do different types of jobs (aside from technical jobs like communications specialists, who always do the same thing) for instance, I think most of the foreign service officers have to do a consular rotation where they're working with people on passport or immigration or travel issues rather than on political or economic issues.

It's also to provide career progression and to prevent burnout some postings are hardship ones and quite gruelling.