What's an incorporated software developer?

Question

I saw a job posting asking for "incorporated software developers" and asking them to state their "incorporated rate" when applying. What's the difference between an incorporated developer and a contractor/freelancer? Google isn't helping.

My best guess is that an incorporated developer is just a freelancer/contractor who sets up a corporation and works as the sole employee of that corporation, rather than freelancing under their own name. But since (I assume) you would have to pay both corporate and income taxes if you did that, rather than just income taxes, what would be the point of doing that? There would be some protection from legal liability, but that generally isn't a big risk for software developers.