Acoustic Guitar Construction

I love the look and sound of the Martin 15 series and other 30's guitars which are unbound. Does it serve structural or acoustic function? I guess a purfling channel thins the top a bit around the perimeter but i can't imagine it makes a big difference. Any thoughts?

Can't imagine one using it to intentionally refine acoustics; I'm sure there may be some who believe otherwise.
Personally, I view purfling as providing an aesthetic element.
Binding covers the endgrain of the plates (endgrain usually finishes differently than the face), so it could also be considered to have an aesthetic function; however, bindings could also be viewed to to serve more than simply aesthetics, as it helps "protect" the edges of both the sides and top/back plates from damage. Also protects purfling if you use it. Sorta like the bumper on a car.

Do as you please. More than a few guitars out there without purfling or bindings.
I like using binding, as I think it is a really great way to either accentuate really good wood or even add contrast to a (visually) less-than-stellar wood.

Here is what can be accomplished with no binding - not mine, I could not yet pull it off - this guy bevels the plates and the rim to get this ultra clean look. I'd really like to see his set-up, which must be really precise.

Thanks for the sensible and helpful replies guys.

I'm sure i read somewhere on the internet that it's the herringbone trim that gives the D-28 it's great sound. . .

Bindings help prevent moisture from entering the end grain of the plates

Binding are made of harder of more flexible material to help prevent dents on the vunerable edges

The binding channels loosens the top along the perimeter to allow the sound-board to be more responsive -- Somewhere on this forum I believe Brian Burns comments of this issue.

viewtopic.php?f=17&t=175&hilit=brian+burns&start=30

guessing you mean this reported conversation.

I found that the resonance of the box dropped and improved with installing the binding but I put it down to thinning the edges of the SB at the same time, guessing it was probably the combined effect.

Yeah, Mike, that's the thread.
It started pretty much like this one- interest in guitars absent of binding, best methods to accomplish, and possible detriments.

In that thread, Ken mentions that rather than thinking of the binding itself as the contributor to altered acoustics, it's the joint created to facilitate the installation of the trim.
In other words, it's probably best not to go thinking that Brazilian rosewood bindings are gonna make your guitar "sound better" than ebony or holly or maple or walnut or whatever.
Matter-of-fact, in order to obtain the "hinge effect" discussed in that thread, one needs to use purfling, and bindings could be viewed as protectors of the purfling.
So here's some food for thought; will a guitar that has bindings, yet has no purfling, provide any acoustical advantage to an unbound guitar?

So after this, why did I mention in the first post "Can't imagine one using it to intentionally refine acoustics; I'm sure there may be some who believe otherwise. Personally, I view purfling as an aesthetic element."?
Since I obviously did not disagree in the other thread, am I now contradicting myself? Allowing further clarification, rather than using the word "refine", I should have used the word "control". I firmly believe that a procedure, in this instance installation of purfling, can be used to refine an outcome, but I do not believe that one can control the result.
I am certainly not in the class of individuals who can determine such minute differences. For that matter, I still have my daughter tap soundboards; she can hear subtle differences, while I cannot. But I can feel different vibration, while she cannot.

There are many fine examples of guitars with both binding and purfling, binding without purfling, and guitars with neither.
If you prefer the unbound appearance, are not concerned with protective advantages, but yet are concerned with acoustical refinement, perhaps consider judicious thinning of the soundboard perimeter.