Contractors and DIY use groovers or saw cut control lines so that the
concrete will break at the joints. That's the plan but more lightly the
concrete slab will crack everywhere except at the joint lines. For the
concrete slabs I saw on patios, driveways and sidewalks, it seems pointless
to have control joints. Expansion joints excepted, off course.

So the question is, when concrete cracks then how do you make it break at
the control joints more often than elsewhere?