Synchronization between two 'local' folders?

We can now open a tab with a local directory on both sides, which is wonderful. However, Commands > Synchronize is greyed out in that case. Is there a fundamental reason why synchronization is not possible for two local directory trees?

The second 'local' directory is generally a mapped drive or a connected device, but there might be times when both directories were really 'local'. What I'm really interested in is a recursive comparison, but that seems to be possible only by asking for a synchronization but remembering to check the 'Preview changes' box.

Thank you.