Great post.
When I introduce new students to side spin, I start by showing them some standard position plays where english makes the shot easy. I then go into my list of five reasons why side spin is hard or dangerous to use: miscue, squirt, swerve, throw, skid. For swerve and throw, I'm careful to show the student how those "problems" can actually be used to advantage. (Even skid can be used to advantage on several proposition shots. :wink
Tin Man and Bob Jewett have it right. Two points. First, while most of us would concede that it is "better" to play all shots on the vertical axis, it unfortunately requires near-perfect speed control to get close to the right angle on every shot. To me that is top professional level, something even good professionals can not do consistently (let alone us mere mortals). Thus,
as a practical matter, English becomes necessary to get back into a better line.
One can of course choose not to use English, and leave yourself a little harder or further away on the next shot -- this is the way some people go. As Tin Man said, it's really about balancing the risk. English makes the shot a little harder technically, but if it makes the next shot easier, then it often becomes an acceptable risk, and the "right" shot.
The second point is that English is ABSOLUTELY required on a not insignificant number of shots, and it also makes another class of shots MUCH easier. It is much easier to make a ball frozen to the rail with running English (at most middle and especially obtuse angles). It is much easier to make a frozen object ball with inside English when the cue ball is also frozen. When you're almost straight into the corner pocket and need to go to the opposite short rail it is sometimes the ONLY choice to pick a position path that "spins" the ball down the table. In fact, whenever I have a choice between power and spin I invariably pick spin, and let the ball do the work. I don't break my arm, my mechanics are more reliable, my stroke is more accurate, and the pocket becomes bigger --- IF you understand the adjustments required, how can this be wrong?
English is also required sometimes to use spin-induced throw to make a ball you can't fully see, or to alter the cue ball's path for position by throwing the object ball. English is also necessary for the deliberate swerve shots that come up often. English is also mandatory many times for kick shots. I could go on, but English is in my view a
necessary part of the game, and I would think it extremely difficult to be anything more than an intermediate player without it. The trick, as Bob said, is to understand the squirt, swerve and throw adjustments required. English is just another tool in your toolbox, and the more tools you have the better.
I can finally add, personally, that I beat players quite often that are a full notch better than me by using finesse to control whitey to a better position. For example, using drag draw and max right (to increase the spin-speed ratio) in order to break out a cluster that simply can not be reached otherwise. English is a very powerful tool for me, and the rest of us elders that no longer have the eyesight and coordination to consistently make those long shots.