Take a minute and look at this picture:
To me, it looks a little … dull. It seems to be really gray. When you want to globally increase the colors of the image, you have two options. You can either increase the vibrance or the saturation.
This is what happens when I set Vibrance to +100.
Notice how the grass is way more green, the stripes on my shirt are way more red, so on and so forth …
To me, it looks more colorful and ‘better’ than the original picture.
Now, what if I were to increase the saturation instead?
Colors are definitely better. Grass is greener, the red is redder. But did you notice that my skin seems more orange? ewwww.
Usually when there are people in the picture, you don’t want to increase saturation by that much. Instead, increase vibrance.
Vibrance increases all the colors but it takes into account flesh tones and tries to preserve them. In the above images, both were set to +100. As always, things are better in moderation. Use your eye to judge what is right. Use vibrance when the subject is a person.