While not rare, kill shots are not really common either. But, they do come up with some regularity to those that are familiar with them an their uses.
Interestingly, with the timing, this topic came up today with a student. This is a good example of what can be done using a kill shot that otherwise could not be done.
This was on a bar table, so the angles are steeper than on a 9'table. Set up an ob 1/4 ball off the side rail at the second diamond up from the corner pocket on a long rail. Place the cb 2 1/2 balls up from the side pocket on the centerline of the table. This should give you a 45 degree angle on the ob. Now place another ob on the short end rail centered.
The goal is to make the ob in the corner pocket and get shape on the ob on the rail to the opposite corner pocket only using one rail. (just pretend there are blocker balls so you can't go back and forth across the table to get down to the ob)
Practice it until you can at least get the cb half a diamond away from the ob and a ball or two widths off the end rail. It's not hard to do, but a good stroke is a must.
The only way to accomplish this task is with a masse' (no need to go to that extreme here) or with a draw-drag shot using english. The draw-drag kills the cb speed off the rail, the cb then spins down table, and the ob goes in at pocket speed.
I think the reason most have trouble with shots like above is because far too many are not stroking the cb correctly. They are trying to hit the cb where they want to, instead of trying to shoot right through the cb . (it's that old accelerate, not decelerate stroke).