I have two things that I've noticed in functionality - one only because support mentioned it. Again, you kind of have to read through the marketing-speak for the release notes.
- Greatly improved dense support structure processing for complex models
So, sometimes with complicated models, Simplify3D would hang or take forever (effectively hang) if you had "too many" dense support layers. In my case, "too many" was 3. Now it seems to work on the same model that I had trouble with before, so that's at least part of this bullet point.
- Improved post-processing script performance
The {STRIP ";"} command in the CubePro profile was the cause of a few headaches for me because it would hang up on larger prints and have no trouble on smaller prints. I wrote a script to handle it outside of Simplify3D, but now it works fine in 3.1.1.