This may not apply as much to written language, but there are benefits at times to pretending to be more ignorant or dumb than you actually are. My father was actually a master at this. He was brilliant in his own ways (not the academic sense, but mechanically and socially brilliant), but had the persona of the "dumb hick" down completely. People would underestimate him, sometimes try to take advantage of him, then he would gently show his competence and they would quickly backtrack and essentially give him whatever he wanted. It's obviously manipulative, but was often a way of catching people in their own trap. Think car dealers trying to cheat him, salesmen, etc. I just can't pull it off as well without seeming fake.

I'm not sure there is validity to either appearing smarter than you are or dumber on a regular basis though, particularly with people you work with. Integrity is a much more important attribute to me in coworkers and employees than either feigned competence or feigned humility. Genuine competence or genuine humility are different matters though of course.