Freehand Cut, the current behavior, allowing the user to draw the cutting path freely.
Straight-Line Cut, allowing the user to click and drag between two points to create a perfectly straight cut.

The straight-line mode could be added as an option in the Context panel when the Knife Tool is active. A modifier key could also temporarily constrain a freehand cut into a straight line.

It would be useful if the straight-line mode also supported angle constraints and snapping, including horizontal, vertical, 45-degree angles, guides, nodes, and object geometry.

This would make the Knife Tool faster and more accurate for technical cuts, lettering, geometric artwork, and production work. It would also remove the need to create guidelines or use other tools just to make a clean straight cut.