To reset the values to factory settings, you can press the + and - buttons at the same time, after selecting the paramater to be reset.
I have heard a couple of duos and trios use the harmonizer to good advantage. I used the 8000 harmonizer with the 6-piece band doing the Miss Teenage America pageant a few years ago.
It works anytime you need additional voices. If the arranger isn't running, you set the harmonizer to Vocoder mode.
DonM