On this video Photoshop expert Jesús Ramirez (from the Photoshop training channel) talks about the differences between saturation and vibrance and a few other related subtleties in Photoshop.
You might think that adding a hue-saturation adjustment layer is a good idea if you want to add some saturation to the colors in your image but as Ramirez demonstrates in the video – this can actually be too much in many cases (even if you limit yourself to just one specific color).
The option that Ramirez suggest is using the vibrance adjustment layer which protects skin tones and colors which are already saturated so you won’t get those over saturated colors and this gives you better control of the amount of saturation.
Now for the million dollar question (or at least the question you want an answer to if you are watching this video), what is the difference between vibrance and saturation – well, according to Ramirez saturation tend to impact all color intensity equally, while vibrance only increases the intensity of the less saturated colors in an image (and as we mentioned protects from over saturation and gourds skin tones).
Do keep in mind one other thing – the examples that Ramirez had in this video about the different amounts of change with both vibrance and saturation are different in Photoshop/Lightroom and Camera RAW so do your own testing.