The PC I have and most of the PCs out there today have multiple processing cores. Mine has 6 with 12 logical threads.
When I select Recalculate All, just one core is used. Each one is processed sequentially.
My current project has 20 toolpaths. Each is independent of the others. They could
be calculated in parallel.
This would take advantage of idle processors and speed up Recalculation quite a bit. It's almost Christmas. This is on my list.