Les Paul's first electric 'guitar' was apparently one wire and it used a steel railway sleeper as the body.
 
He said it was the most beautiful, pure tone he'd ever heard.
 
...but was equally practical as the granite guitar ;-)
 
Also, as an ex-chef, isn't a granite chopping board rather hard?  Still, as long as it's not glass...don't get me started there..!

ston as an ex-chef, isn't a granite chopping board rather hard?  Still, as long as it's not glass...don't get me started there..!

I'm not an ex-chef, so I'm not as qualified as you, but yes it is very hard. Hence I'm not going to even try turning it into a guitar body...

Lots of solid body guitars are more than two pieces of wood. I don't it matters as long as it sounds good and looks good. I'll buy a cheap guitar online but never a nice one. I have to play them all, unplugged. See how they feel and sound unplugged. If it does not sound good unplugged it isn't going to sound as good as it could plugged in, unless of course you are using so much distortion or other FX that you can't hear the tone of the guitar.
I don't think I've ever actually seen a one piece guitar. I've seen one piece necks but they have to be cut just right so that they don't warp.
The tone is why Gibson uses a light nitrocellulose finish. A heavy paint job sucks some of the tone away. The Gibson Historic RIs also have a longer neck tenon that actually enters the top of the pickup cavity. This also lends to a better tone. Lots of things go to tone. Like the big flat bridge on a Telecaster and the neck through strings. Put a Stratocaster bridge on a Telecaster and it will sound different. Lots of stuff going on. I imagine the most important wood is the wood where the pickups are and the neck connects to the body and then the neck itself... and the fret board. I prefer maple on a Strat (I like the look) and I like ebony on a mahogany body and neck guitar (the tone). Rosewood is fine but ebony will last a LONG time.
I have some guitars where you can see the different wood pieces. With a thin coat of paint you usually can, especially from the back. Most Fenders though, you can't see through the paint. I think they are routinely 4 to 5 pieces of wood, maybe less in CS guitars... I'm guessing though.
None of it matters if the guitar sounds good, feels good, and looks good and most important you like it! If you like it you will play it more and play it better.
J

Dammit, Spacey. Ya stubborn bastard... get back here!!!
 
We needz ya!

jbow
The tone is why Gibson uses a light nitrocellulose finish. A heavy paint job sucks some of the tone away.

This is complete nonsense.
 
On an electric guitar, what matters is the relationship between the PU's and the strings. Finish simply has no affect on this regardless of common mythology that any little detail must matter. The desire for nitrocellulose is a combination of aesthetics, perhaps the feel of it, and of course vintage mystique.
 
Finish plays a role with acoustic instruments as it can meaningfully affect the key factors of strength vs. elasticity of, say, an acoustic guitar top.
 
There is a common belief among some that the same rules apply acoustic and solid body instruments, but it's wrong. On an acoustic instrument the string energy is translated into acoustic sound by the top (and to a lessor extent the back and sides) vibrating up and down as a diaphragm. The key factors are for the wood to move as easily as possible (elasticity) without breaking. On acoustic instruments, one wants to use a finish that enhances rather than impedes these factors. 
 
But nothing like this happens with a solid body instrument - the physics of a thin piece of wood vibrating up and down are completely different than vibrations traveling through a solid piece of wood and arriving at a boundary. Which is exactly why solid bodies make for such terrible "acoustic" instruments. 

Out of respect for two old friends and at the risk of having my words changed I will post my views.
 
First, if the OP did indeed see a luthier cut a one-piece body blank in half and then glue it back together I'm at a loss to explain why. It makes absolutely no sense to do and in fact could cause more problems.
(wood has stored energy and when you make major cuts in it you may see it twist and bend)
 
Others have offered reasoning and I have no intentions of changing their beliefs.
 
The topic has expanded to include electric guitar tops and acoustics but I will address the use of a one-piece body blank and multi-piece body blanks for electric guitars. ( not necks)
 
One piece body blanks and multi-piece body blanks have been used since the beginning and will continue until....well I don't want to think about that but I'm sure you know.
 
The reasons are because consumers have choices based on their beliefs and what they like to see.
If there were problems or big advantages with either then the market would reflect it and at this time there is nothing in the market indicating anything other than both work very well.
 
I don't think one is better than the other for building or after they're finished although sometimes I feel like a play a black one better but then I play a red, gold, silver and figure now it really might be which day I play the black one and I break out in a sweat and think, “why is everything so hard?”.
 
They're wood. Both methods are easy to build with and both will be fine if you take care of them and don't expose the wood to harsh environments. Everything else is whatever belief you fancy that helps you feel better about spending your coins and makes you feel like the guitar is “special”.
 
Just don't go cutting one-piece body blanks in half and gluing it back together for any reason...it just makes you look stupid.
 
I'm done and hope I'm not a stubborn bastard anymore Beep! LOL.
Maybe another year and I'll have more BS to print. Bye and take care Mesh and Beep.
 
P.S.
I couldn't help but think....players are buying guitars that are beat to hell and crap finishes to look bad and aged while others are pointing out how one type might warp? I'm going back to my planet.

Yay, Spacey!
 
And yeah... seems if you have a solid hunk of good, properly dried and handled wood that would be more desirable that lopping that piece of wood in half.
 
However I'm going to assume the "good" and "properly dried/handled" part is where things go screwy (or more accurately time consuming/expensive).
 
The routing/drilling angle stuff makes sense too. Easier to make all those holes that way.
 
Sounds like a combo of cost cutting and laziness.
 
But... people wanna pay $300 for a guit then what can the manus do?
 
Take care dood. Come back soon.

Good to see the space man lurking about. I miss his how-to postings very much.

Michael!  Good to see you back at the asylum. 

spacey
Just don't go cutting one-piece body blanks in half and gluing it back together for any reason...it just makes you look stupid.

Unless you're putting a neck that runs between them in the middle. 
 
Good to see you back for a visit.