Digital Vibrance is artificially boosting colours to try and make them look better on typically dull LCDs, not good for accuracy, but many people prefer it. It's like Sony's VIVID setting it oversaturates the h3ll out of stuff, but go into more stores and put two TVs side by side set them properly and then switch the Sony to Vivid and most people will choose it even if it's no longer what was supposed to be displayed based on original content. Same thing here usually.
So leaving it as off as a default is a good idea, but the do need to remind people the feature has returned (after a hiatus during the G80 year).
Only for people doing picture editing or something that requires accuracy, set up your colourimeter and then go with that.
For other people, nah, go with whatever looks good to you, but also realize that it may look cool, but it indeed may be more cartoonish or oversaturated, etc.
It's like touching up a photo, the original may be accurate but someone's skin tone may be to pale and look better with a little photo-chopped sun-in. I think it's a matter of taste, whatever works for whomever. I go out of my way for accuracy, but that's not always what makes a movie or game look the best.
One thing I noticed that in nvidia control panel is the overlay colour is limited by default. If you unlock all the colours you'll all see a huge difference in terms colour. I don't know much about their latest cards. I changed this setting on a 7 series using 178.24.