Hey, got this off
http://www.guitarsite.com/guitar_FAQ.htm
It's a good description. Hope it helps.
What's the difference between set, through, and bolt-on necks?
I have heard some rumblings that bolt-on necks give a more open sound, but i don't know if i would agree with that entirely. if a bolt-on neck is bolted as tight as possible, you're not going to lose any sustain compared to a set-in neck or a neck-through design. bolt-on necks obviously have the advantage of being replaceable and easier to work on for fret jobs or refinishing, but i DO think they have their own tone, with perhaps a bit more overtone content than set-neck designs.
Set-neck designs are great in the fact that they transfer sustain well and have a lot of fundamental content--however, they also are harder to make correctly, and if the neck is set at the wrong angle, it's going to be like "polishing turd" when doing the setup because the luthier will have to compensate by milling some frets lower than others to compensate. also, the intonation may be altered and affected adversely as a result.
Neck-through designs are very solid and have the benefit of lacking the clumsy block that sometimes results from the other designs, but if a guitar has a maple neck (and most do), the tone of the guitar can be very bright, since the pickups reside right on a block of hard rock maple. the other disadvantage of neck-through designs is that once you damage the neck, it's very expensive to fix the guitar.
In any event, the bottom line is that it shouldn't matter how the neck is joined to the body--if it's done correctly, you're going to have a killer guitar.