I'm not currently sanding anything. I was just curious about the Festool sander vs the PC sander, which I have a fair amount of experience with.
Unlike a top-notch finisher, I typically don't have enough opportunity to hone my finishing abilities. In fact, I know of one finisher who sands very little, or not at all in some instances, because it isn't needed. I, on the other hand, am not anywhere near this good of a finisher, as I don't have the opportunity to do so. I might have a large job that by the end of it I have gotten pretty good, then it might be 6 months to a year later (maybe longer as I would typically sub out larger jobs) before I get another job that requires the same skill level to finish something, particularly to a L-5 finish.
To have the right equipment would probably help me more than anything else in finishing up something that I probably botched the tape and mud somewhat to begin with.