Countless pieces of untradable gear fall into the hands fo players that don't really have any use for them except for converting them into Grand Company points. On a typical Expert Roulette run, what are the odds that one of the four participants has Armorer Desynth leveled high enough to convert those Sabatons of the Divine War that drop? Probably not high.

With Request Desynth, the recipient of those Sabatons has the option to seek out a crafter to desynth them for the chance of getting a valuable item to sell. The crafter's motivation could be skillups, a fee of some kind, or whatever. This would greatly increase the amount of Demimateria available on the marketboards. While it's true that this would also greatly devalue that Demimateria, I still see it as a positive thing. Right now, demimateria is just too scarce - pretty much ANY items involving recipes that include demimateria are priced like luxury items, even when they were clearly intended to be generally available.