(This isn't aimed at anyone on this board, it's a rant over discussions I've had elsewhere.  I also have questions at the bottom)

Maybe this is a small thing to get my panties in a bunch about, but that's what im good at.  Had arguments, had discussions, done math, had others do math, put in a lot of thinking time, and am still coming to the conclusion that moving forward or backwards to carry a pin is antiquated, illogical, and a complete placebo.  Let's look at the math first.

Assuming a common house shot line of a release on the 18 board, with a breakpoint target of 5 at 40 feet (a line that also makes the numbers rather generous), moving back 6 inches on the approach (also assuming you're a robot with laser precision) changes your launch angle a tenth of a single degree, resulting in you placing the ball down in the neighborhood of 3/4 of a board right, or appx the 17.25 board.  Considering that moving back on the approach doesn't magically make the pattern shorter (which really got the panty bunching started, completely illogical), even if you were laser precise, ignoring ALL other factors, this move is completely insignificant and astronomically dwarfed by the standard deviation of human consistency. 

The belief that moving back 6 inches will get the ball to roll/hook 6 inches earlier is .  . interesting.  It really depends on what the ball roll is doing in the first place.  If you're leaving flat 10s because your ball is rolling too soon and bleeding energy, moving back 6 inches would theoretically cause the ball to roll even earlier and bleed more energy.  Factoring in the coefficient of friction, something that has more to do with when a ball rolls and hooks than anything else, 6 extra inches in oil amounts to what gained?  Because most people lay the ball down at varying places past the foul line, you could either be adding 6 inches of oil (for example, if the pattern is 40 feet long, and you normally lay the ball down a foot past the line, resulting in the ball traveling through 39 feet of oil, if you back up 6 inches, you're just making the ball travel through 39.5 feet of oil now) or if you lay it down early, you could be adding 6 inches of dry, unoiled approach BEFORE the ball gets into the oil, something that could change the trajectory of the ball. 

The effects that moving back ACTUALLY has?  Depending on how many steps you take, it could add 1-1.5" inches per step to the length of your approach on average obviously, and that's only if you intend to end up sliding in the same place.  If that is the intent, or the result you're going for, the move is absolutely irrelevant, ineffective, and insignificant.  However, if the intent is to make your steps longer or speed your feet up, depending on the current quality of your timing, that could help or it could hurt.  Walking faster or slower can change all manner of things in your timing which add MANY more variables which result in more changes than just getting the ball to roll 6 inches earlier.  If THAT is the case, I have no idea why someone would want to use their entire body and slightly alter many different mechanics to achieve something that a much smaller, more localized adjustment could fix. 

To me, after looking at the logistics of it, it's an old antiquated idea along the lines of angling your thumb back to get a cleaner release.  It's a basic random thought that will drop into someone's mind that sounds plausible at first, but upon further examination really falls apart.  It's into the placebo realm, it's tricking your mind into believing something simple will fix a problem, which makes you more comfortable and relaxed, more often than not resulting in a better quality shot.  Because I can guarantee you that if you back up 6 inches on the approach, you won't throw the same exact shot next time, you won't end up exactly 6 inches further back on the approach, or if the intent is to add length to your steps, you won't end up exactly where you normally do.  You know how many repetitions you need to change a mechanic, or how many times you need to do something to erase old muscle memory and create new?  And you really think this is going to work perfectly the first time?  What other mechanical adjustment have you ever learned that worked the first time?  This reduces the reasons it would work to being placebo or coincidence. 

Anything I missed or left out or didn't consider?

You could write a book……..oh, wait………you just did.

Moving up or back on the approach is a valid adjustment for poor carry. However, most bowlers don't realize why. Moving back should result in increased ball speed, resulting in a breakpoint further down the lane. Moving up should result in decreased ball speed, with an earlier breakpoint. It's just one of many adjustments that are available to those who understand ball motion (or those of us who pretend to).

Gizmo I have been fighting this concept at my center. Many bowlers have been taught that moving forward or back is the only type of adjustment to make.  I have given up on trying to argue the point, I choose to ignore it when I hear a kid using this method because his dad told him.

my dad is another one that believing in the moving up and back on the approach and he still doesnt believe me when i tell him its a psuedo adjustment. i even show him i normally slide 1-2" behind  the foul line. obviously i cant move up anymore, i move back 6" on the approach i still slide 1-2" from the approach but i end up carrying what used to be a ring 7 pin so the adjustment "worked"

I use moving forward and backwards to adjust my speed more than anything else.  I tend to end up at the same place, so that small move will change the size of the steps and slightly alter my ball speed.  I admit I started doing it years ago for the old fashioned reason, but when I saw what it really did for me, there is still value to it.

I move back on the approach to get  the ten pin out works great for me.

It doesn't matter if it is the "best" adjustment or not if it knocks the pins down it worked. The only thing that matters is the score at the end of the game. Not how you get to that score.

Moving slightly forward, or slightly backwards, can have several different effects on your shot, but will be much independent for each bowler. As in all cases, for each individual, the results can be quite different.

 For me, it is an adjustment I make when I continually leave the same single pin spare, like a tenpin, or a four pin.

 As best I can figure, the biggest thing it does for me is slightly change my launch angle, thus changing the way the ball reads the pattern, which usually gives me a slightly different entry angle. It doesn't always have the desired results, but sometimes it is the correct choice.

 As with all other bowling adjustments, it will not always work, and will work for some people better than others, depending on many "intangible" elements.