This one's been debunked by others already but, I'll repeat it anyway for those who may still think it's a fact. Satin finishes are thinner and promote more resonance (this one's popular for sellers offering acoustics). Not true. Satin finishes became popular on electrics first to add to their visual appeal, most blurbs in catalogs stating that it gave the instrument the look of  'a worn but well cared-for, cherished original' or words to that effect. Acoustics adopted it for similar reasons. I'm assuming that the 'relicing' rage didn't work as well on acoustic guitars as it did on electrics, so a dull finish imparted that same 'vintage vibe' to acoustics without actually damaging and scratching up the instrument in an attempt to simulate the aging process. The truth is, the satin finishes are generally the same thickness as gloss. A satin finish is also a cost-saving measure to guitar companies as the instrument does not require the final buffing out of the clear coat, a labor-intensive process that adds to the retail price. Any extra resonance that might gained by a thinner finish would be so negligible, it would not be within the range of our hearing. Very sensitive measuring equipment (and, possibly, small dogs) may be able to detect a difference but not any of us normal humans. Another myth - thin finishes were applied to vintage instruments to give them better tone and more resonance. Not quite. Clear finishes on vintage instruments, nitrocellulose and lacquer in particular, are prone to running and peeling if applied too heavily so they were thin in order to provide good protection for the wood and paint or stain while preserving the instrument's attractive appearance. Thinner coats also dried more quickly and thoroughly, speeding the building process and reducing costs. Lacquer and nitro, in particular, are very flammable substances and dangerous to work with so it's reasonable to assume guitar manufacturers tried to reduce the risk of accidents by keeping the application time of these finishes to a minimum. The thin finish was a compromise for this as well, providing adequate protection for the instrument while reducing risks for employees engaged in applying the final clear finish.