The bodies made out 1-piece, the neck union with the body, can be done in 2 ways: (1) screwed which is called "Bolt-on Neck" or (2) glued that gives more sustain to the instrument, which is called "Set-in neck".
The bodies made out 1-piece are instruments more rigid than the ones made out 2 or 3 pieces, because the sound and resonance is more compact and brighter. The more pieces that make up the instrument, it will have a greater stability, but the sound of the guitar will always be better the fewer pieces we use, since the vibrations transfer is better in one body.
There are many factors that influence the final sound of the guitar, but a good wood choice for the instrument, will contribute positively to achieving the desired sound.
