But -- is the evil in the world organized and unified, or not?
Chaotic evil has the disadvantage of not being able to attain levels of scale that lawful evil can, and it being much easier for the good guys to pit one evil against other, but then again, it doesn't have to work with the inherent problems of unified evil requiring internal good (the evil beings of an organization must be able to trust each other, be loyal, work together, tell each other the truth, etc.to at least a degree), and if its neighbor evil is destroyed, it can go on, untroubled. Which makes plotting more difficult, since you don't want it to get episodic.
Not there's an abyss between them. The Lord of the Rings put forward a lot of pure chaotic evil -- on top of the infighting that is an inherent problem with lawful evil -- such as Old Man Willow and Caradhras.
But the big difference between them is thematic. Chaotic evil means there's always another evil lurking around the corner when you've finished off this one. (Useful for series, no doubt.) And so the endings are more ambiguous.