When you buy a readymade shirt, it is quite possible that the sleeves are slightly short, or slightly long, the collar is tight or loose, or overall shirt length is a little too much, or a little less. However, when a tailor stitches your shirt, such problems can almost never occur because the tailor stitches the shirt to YOUR dimensions.
Acoustic guitars – of any brand – are made much in the same manner and unless they are ‘tailor-made’ to suit you and your playing style, they can never give the output that they are capable of, and you can never enjoy them completely.
Once an acoustic guitar is set up, it can dramatically improve its volume, sustain and ease of playing. Here, I might add that my experience has been that, after a set-up, generally, a big-name instrument improves by leaps and bounds in comparison to a not-so-known instrument. That said, it does not mean that only high-end instruments need a set-up.
The bottom line is that a set-up does always help an instrument play better.
As an example, here is an Epiphone Hummingbird (a lesser creature than its famed sibling, the Gibson Hummingbird), which I had the pleasure of working on recently.
It was a well-kept instrument: not too old, but it was clean and had a hard case to live in.
The instrument was in for a set-up but I also managed to convince the owner to swap the plastic(-like) material nut and saddle with bone elements.
But as I pulled out the saddle and lifted the piezo element, there was something hiding there that should not have been there in the first place. It was removed and its thickness was added to the bone saddle.
As I went about cleaning the instrument, I heard the odd but familiar rattle inside it. I turned it over and shook the ‘rattle’ out of it.
I cleaned up the fretboard some, oiled it and polished up the fretwires
Strung up with strings chosen by the owner, I gave them a stretch with the ‘String Strecha’!
So, in this particular case, what a set-up did was enhance the existing sound quality of the guitar while maintaining a good, low but clean action. In the process, it also got its fretboard cleaned and nourished, and got its fretwires polished to a pretty sheen.
And that was a wrap on this beauty!