Crystal vs Caramel-- What is the Difference? What is their Function in the Mash Bill?

[GrowleyMonster]

Crystal vs Caramel-- What is the Difference? What is their Function in the Mash Bill? What is their Effect on an Ale? I am asking because I don't think I fully understand this topic and I am trying to hammer it into my brain cells because those types of malt are I am sure very useful. Right? Is there a limit to how much I should use, and why?

 

[PCABrewing]

Breiss has a nice write-up here:
Is it Crystal or Caramel Malt? - Brewing With Briess