Vis3 is the new version of map visibility that was kindly given to us by Valve to keep us more up to date with their current engine. They take the time to help us integrate new features which is very much appreciated.
It is worth noting that this isn't a miracle solution to large outdoor maps but a good improvement compared to the old Vis2.
Compile times for map vis should be improved, we were seeing a x6 improvement when compiling our Construct map. It does this while creating a higher voxel resolution and reduced file size.
Runtime performance hasn't been fully tested yet but I'm interested to see what gains people see there.