The reason for the "f holes" is well known. For an instrument that depends on a resonant air cavity in the body, the "air resonance" frequency is proportional to the total area of all the holes, divided by the volume in the cavity.

Instrument makers believe that "tuning" the air resonance of the body is extremely critical to achieving proper "voice" for the instrument (although there's little real agreement about what it should be tuned to) and the final tuning is done by "trimming the holes" to bring the air resonance pitch up to a satisfactory frequency.

It is extremely difficult to trim a round hole precisely by small increments and keep it round, so if much trimming is done it ends up ugly. The "compound curves" of the f-hole can be shaved a bit here and there to change the cross-section area of the hole and still retain the "same general appearance" regardless of how badly they're butchered in the process.

But the real reason for putting f-holes on a guitar is that they're used a lot on fiddles and other classical instruments, so the guitar carpenters think it makes the guitar look like something classy - Like Man Ray's "Ingres' Violin" perhaps.

John