[DF] Why is the Prime Material Plane Important?

[roguebfl]

Originally Posted by Purple Haze

If one is going to discuss a D&D/Gygaxish cosmology, the Prime Material Plane was never unique, any book referencing it also contained reference to Alternate Prime Material Planes, the number of which was implied to be large.

I recall it as referring to Alternate Material Planes with Prime being reserved for only he campaign's home plane... that is to say an any given campaign there was only one prime the rest were all alternate.