When I was taking my learn-your-machine class, the instructor said that if crummy thread, including the poly thread sold just for sergers, was used for any length of time it could leave a residue on the tension disks. She also said that if that happens, it meant a repair man had to clean them.
I don't know if this is true, it doesn't sound reasonable to me. It also could have been advice specific to my brand of machine, but I haven't seen it written down anywhere in any of the literature for my machine.
She may have been passing on an "old wives tale." She was sort of a nut! LOL...
Anyway, I don't use thread made just for sergers in my sewing machine. I prefer cotton.