Knife tool - if faces are selected, only cut those... if not, cut everything

It would be cool if the default Knife behavior would take into account whether any faces are selected. Right now this functionality can be enabled only by changing the setting in the Input menu for the Knife hotkey, so if you want to cut only selected faces, you have to have a separate hotkey for it, I think. Also if you enable Cut Only Selected Faces in Input, the Knife tool will give an error if you don't have any faces selected...

Knife should check if any faces are selected and if so, only cut selected faces. If nothing is selected cut across all geometry.