Whats up with Blue DEF?

[Phillytwotank]

Diesel Exhaust Fluid. Been frequenting this forum for a couple years now and i don't recall ever seeing much discussion on the topic.

so i'm throwing it out there.. I don't have any practical experience with the stuff but i do know generally what it is.

What is it good for?
Could a system be installed after market? Why would one want to do that?

Discussion GO!