PMD and what they are used for... "Use External Binary Morph Targets: Checking this box will enable the use of External Binary Morph Targets (EBMTs) when saving new content, or resaving legacy Poser files. Saving legacy figures to the Poser Library with this option enabled will generate new .pmd EBMT files for those figures, thus allowing you to take advantage of morph target sharing, reduced file sizes, and faster processing speeds for your legacy figures."

I must remember to remember what it was I had to remember.