Despite Photoshop being installed on D:, the cache and various settings and temp files are in C:, my C: drive is a very small boot drive and fills up quickly with smart object .psb when working on a large project, which causes Photoshop to be unable to save my working document when it fills.
This doesn't make any sense, I'd rather the temp was on another larger drive. When I have tried to manually move the temp folder location to a larger drive, Photoshop crashes and will not load.