Mat pose files started back in earlier versions of Poser - there didn't used to be a material room, if I remember correctly.  I think Poser 6 was the first version with a material room, but the material folder didn't show in the Poser Library till Poser 8, so you couldn't access it from the Pose room in Poser 6 or 7.  In the 2 earlier versions, you had to go into the material room to apply mt5 or mc6 files.  I have Poser 6 on my computer for testing so have to do that when I want to apply materials, but it can be done)

There ARE some situations where it makes sense to include pz2 mat poses (since it's so easy to convert from one to the other, for these situations, having BOTH is a good option)

a) if the product is meant to work in Poser 5

b) if the product is meant to work in DS 3 - you can not view mc6 files in DS 3.  I can't recall if it was DS 4 or 4.5 that added the ability to see Poser mc6 files.

For newer products, like the Poser 8+ native figures, and others like Dawn, which require either Poser 9+ or DS 4.5+, there is really no reason to use .pz2 mat files. 

In fact, I've talked to newer Poser users who find it confusing to find materials in the pose folder.  The Poser figures themselves and Poser versions of other products like Dawn, the HiveWire Horse, etc, use ONLY mc6 files, so that is where newer Poser users expect to find them.

Cheers,
Alisa

RETIRED HiveWire 3D QAV Director