I’ve used pianoroll scrubbing a lot previously and it makes life so much easier when working with complex harmonies and passages. To be able to easily and quickly audition the work in detail.
The idea is that only the notes that are visible in the key editor get auditioned, not the whole project. You drag the playhead around with the mouse and the notes under it get played.
This would need to be mapped to a keyboard shortcut to be really useful. For example hold Ctrl-Shift and drag with left mouse button to scrub.