Sorry to post, but I thought I would have a couple of points to bring up.
1. Wood expands and contracts with temperature, but more with humidity changes. If it were just a temperature change, the probability of checking on nitro finished guitars would be quite low. The real factor that causes the checking is humidity. Everybody associates checking with cold temperatures, but the reality is, the colder the temperature, the lower the moisture content capacity of the air(humidity is always measured in relative terms). When a guitar is very cold, and is brought into a hotter room, it will begin to take on humidity, much like a dried out guitar will take on humidity and (hopefully) regain its properly humidified shape. However, when it is going from a cold environment (=low humidity) to a warmer one (=high humidity) suddenly. it will begin to take on water and expand much faster. The vast majority of this expansion is due to the expansion of the white wood between the grain lines of the wood, and much less (actually almost none) will be in the grain lines. Expansion is linear (i.e. each inch of wood width (perpendicular to the grain lines) will expand by roughly the same amount. So a piece of wood, 1" wide will expand by X amount with a humidity change of say 30%. the same piece of wood, 2 inches wide, will expand roughly 2X (assuming quartersawn wood). This isn't an iron clad rule, as wood is a non-uniform material, so changes in grains per inch, and the actual piece of wood will impact the expansion rate, but it will always be true that a wider piece of wood will expand more than a narrower piece of wood. Expansion and contraction of the soundboard wood, in many cases, is why braces come loose or unglued (aside from other factors like impact, insufficient/improperly glued joints, and poor quality or just bad glue). Hardwoods do not expand and contract at the rate that softwoods (including all forms of spruce, cedar, and redwood).
2. What we know as Nitro cellular lacquer comes from either trees, or insects (insects in the case of guitar lacquer, from trees in the case of Chinese lacquers). In its natural form, it is solid. It needs to be dissolved in something, and many solvents have been used, as well as other chemicals to make it easier to spray (often called plasitcizers), and things like retarders to increase the time that it takes the lacquer to dry to allow the humidity/gasses to escape before the nitro surface begins to solidify. Given enough time (very variable, depends on things like initial concentration, ambient humidity, temperature, thickness of finish, etc.) the solvents and other chemicals will evaporate, because they are volatile. The lacquer finish (almost entirely solids now) will be more brittle, and will tend to both be thinner and harder/more brittle than when initially sprayed, it will also be microscopically lighter. This process will be ongoing for many years, in many cases, for the rest of the life of the guitar.
Given the above, lacquer checking will be more prevalent with older guitars, and the tops of guitars (if made of softwoods) will check more than backs or sides. There will be a lower prevalence of checking on backs and sides, and on the tops of all mahogany guitars.
As for tone, while a lot of well respected hand builders and guitar factories have changed over to either catalyzed or poly (-ester or -urethane) finished, without the impetus of local regulations/codes on VOCs, lacquer would probably still be the choice of almost all guitar builders, large and small. Many simply don't have a choice, as the regulations either simply don't permit it, or the cost of a fully compliant nitro lacquer spray booth are simply prohibitive. Even in California, whose regulations are amongst the toughest, Fender's custom shop electrics are still often sprayed with nitro. Hand builders up here in Canada are mostly spraying nitro, because both the regulations are such that they can, and if they do, the requirements don't result in needing to build a cost prohibitive spray booth. Also, being hand builders, they can take the time to do a good job with the finish, allowing sufficient drying time, without the pressures of needing to get X amount of guitars every day. Factories need to produce guitars on a schedule, at a low enough cost to ensure that they are cost competitive and profitable when sold. Anything that helps this process will be used as long as the general public finds it acceptable. So, Taylor can spray a UV catalyzed finish in order to save time, and speed up the process, even though the capital investment is quite substantial, because they can spray catalyzed lacquer, and have it UV cured in 30 seconds. They are less able to afford the month or so that it takes a nitro lacquer guitar to dry to the point where a final polish is possible.
Sorry if I am sounding like I am venting, I don't mean it to sound that way.
Kostas
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