D&D Magic Theory

[Florian]

I've never been a big fan of extraplanar content in general. There's plenty enough to get excited about on the material plane without needing a plane comprised entirely of fire (which was mostly nonsense anyway).

Depends on much you value verisimilitude/are part of the Sim crowd. It´s not a bad thing to be able to keep the power level/fantastical stuff on the prime on an easily digestible level, by having the whole really high fantasy stuff take place elsewhere, preferable other planes that are intentionally different than the Prime.

I think 4E actually broke the game more or less down into three phases, corresponding with character levels: 1/3 Wilderness Exploration, next 1/3 Dungeon Exploration, last 1/3 Outer Planes and stuff.

I don't see why the transitive planes are needed; they're basically an answer to a question nobody asked

For D&D, they were apparently used to model physics. In PF, Transitive Planes have been tied more closely to the mythological functions of the multiverse, along with the Inner Planes.