Photoshop - Vibrance vs. Saturation

I used to wonder what's the difference between Vibrance and Saturation. Both seem to add color to a photograph.
Saturation has been around a lot longer in Photoshop and I knew to use Saturation with caution as it could quickly ruin a photo.
In this train photo, I'd like to add more color.

 

I'll first start by adding Saturation by going to Image - Adjustments - Vibrance. You note that both tools of Saturation and Vibrance show up here.

I'll add too much Saturation to get my point across.

 

What Saturation does is to add color everywhere in the photo whether it needs it or not. Notice how the yellow that was prevalent is now way over done. This is one reason I don't use Saturation much.

When you use Vibrance, you are equalizing color through the entire image.  Colors that were muted are made more vivid while colors that are prominent get ignored.

 

Colors that needed help were boosted. I can increase colors quite a bit before it looks artificial. 
So, the next time you are looking at boosting the color in a photo, reach for Vibrance and ignore the Saturation.