Based on a normal coilver, where just height adjustable
Pro's
* Can go lower
* Can get better handling
* Smaller damper/spring radius means wider wheels (inside)
Con's
* As height determines damper travel, can get rubbish handling if very low
* Hard to set up properly to equal heights
* Rear camber will go out loads when alot lower (so you need camber plates/shims)
As long as you are not stupidly low, they can be advantageous, unless stupidly low is what you want (which I did, so didn't care too much for handling, but didn't want dangerous).