Sauce (particularly on ribs) can add to the appearance score if put on well, can add to the tenderness score ever-so-slightly, and can enhance the flavor of the meat. However, if not matched well with the spices you use in your rub it can hurt the flavor of the meat. Or, too much sauce can take away from the flavor of the meat by dominating it. Not all judges will take off for this (even though they're supposed to because it's a meat contest not a sauce contest), but many/most do.
I think the perfect set of ribs un-sauced can compete well with the perfect sauced set of ribs. However, if your ribs aren't perfect, I do suggest placing a little of your sauce on it, if nothing else to help bring up those appearance and tenderness scores. Again though, some of this may be regional. I'm in a region where un-sauced is perfectly acceptable. I understand that out in the middle of the country that may not be the case.
Down/around here, from what I've seen win more often than not, the pulled pork un-sauced wins more often. However, like above, if the pork isn't perfect, a little sauce can help. This could be very regional though, like I said above. I'm in a region where chopped doesn't play very well. Frankly I can't think of a competition where it won; ever. Sliced is ok if mixed in well with pulled (again, that's here in this region and from what I've seen, averages being averages). Pulled is preferred. I've seen slices that were awesome but they had pulled or chopped and brought the overall box down. I've seen lots the other way too, great pulled but the sliced was tough, and brought the overall scores down.
Great pork wins. Only put the best (you have that day) in that box. The other, leave it on the table for samples.