You select "C Major" and hit OK. Audacity moves every note to the nearest C Major note. Sounds great in theory. In practice, a blue note (like a bluesy flat third) or a passing tone gets snapped to a diatonic pitch, destroying the emotional intent of the performance. There is no option to "keep chromatic notes" or adjust sensitivity per note.
This is where the review takes a downturn. If you are trying to gently nudge an off-key vocal performance into tune without the listener noticing, Audacity is a struggle.