This was asked by a newbie friend of mine and I'll admit I actually didn't have a good answer for this (enough to satisfy him anyway). If, say, I'm shorter or have longer arms, I may be a candidate of shortening my clubs, say, half an inch or an inch. But how does really make a difference if all my clubs are different lengths anyway? I mean, aside from the loft, is there some fundamental difference between a 7 iron and a 5 iron that has been shortened to be 7 iron length (so, same length, different loft)? If I can get used to swinging a (standard length) 5 iron, why couldn't I similarly just get used to swinging a 7 iron that is the same length and build my swing around that (just as much as I would have to build my swing around a 5 iron length, if I needed to)?
Granted, I know "building your swing around your clubs" is the total opposite of what you should be doing, but I'm asking this more on a theoretical level. If I could physically learn to hit a 5 iron (with the length being what it is), why would it be inefficient or suboptimal for me to swing a 7 iron that is the same length? Why is it any more ideal to shorten the club (if the fitting or measurements say I should)?