D&D General Differences Between Limbo And The Far Realm?

[Yaarel]

Limbo
= extreme individualism
(strong distrust against social expectations, but strong loyalty to other individuals)

Farrealms
= insanity
(occasionally the insanity might offer a creative solution to an ongoing problem)

 

[Yaarel]

Limbo has more in common with the Elemental Chaos than the Far Realm, IMO. In my approach to the Far Realm, it’s literally impossible for a mortal’s mind or body to survive traveling there. It’s the realm of extremely alien and incomprehensibly powerful eldritch beings. Limbo is more of a sea of evershifting elemental magic than of Lovecraftian madness.

As I read it, all of the Neutral Planes − Limbo and Mechanus, and Outlands − are part of the "idea" of the production of matter. All three intrinsically entangle the Elemental Chaos. Limbo is like particles, Mechanus is like waves.

I feel it would be more helpful to refer to the Elemental Chaos as the "Elemental Flux". In D&D, "Chaos" is a technical term that refers to something specific relating to ethics.

 

[Li Shenron]

Why would we necessarily need a Far Realm when we have Limbo?

You absolutely do not "necessarily need" either. This sort of "problems" are only problems for people who make them a problem, for example because they pretend the only way to play the game is to include everything officially published or part of core at least. In your games, you don't own these people anything. You can use Limbo but not Far Realm, or viceversa, you can use neither or both, and in that case you can make them as similar or different as you wish, including make them one.

The reason why we have both in the books is only historical: the Far Realm is explicitly inspired by Lovecraft tales, the Limbo is the default plane for "chaotic neutral" alignment in the Great Wheel, whatever idea came to mind to those in charge of the original task of filling all the alignments combinations for the Planescape setting, then further updated in later editions to whatever variants suited the WotC designers at that time.

Outside theorycrafting, none of these matter until the player characters have something to do in these planes in one of your adventures. And even then, you don't even owe your own players a theoretical explanation of any sort: if they want to know more, it's up to their characters to investigate/research and figure things out.