As other people have said, MAT poses (and MOR poses and sub-dividing MAT poses) were originally a hack on the cr2 file. But when the file was renamed with a pz2 extension, Poser would apply the MAT or MOR as if it was a regular pose file.

Then, because pose folders were filling up with MAT poses, people found that they could change the extention to cm2 and fill the Camera library with MAT poses. (This is also why camera files can include code to hide and show the walls of a room.)

In Poser 5, e-frontier decided to officially support MAT poses by calling them material files, but these just affected one material. In Poser 6, the full material collection file was added. And in Poser 9/ Poser Pro 2012, Smith Micro made the materials library available without needing to go into the Material Room.

To me, arguing over MAT poses and material collection files is like the arguing which version of Microsoft Word is better: the one with the usual File, Edit, View menu or the version with the ribbon. Many people are used to the File, Edit, View menu, but they should move on and get used to "progess", right?

And, of course, content creators can't win: for every person who says they want the "new way" of using material collection files, another person will say they prefer the "old way" of using MAT poses. Should a product zip file contain both MAT poses and material collection files? No, because then customers will get confused and ask which files they should use.

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