When you put supporting files in your Poser presets library- meshes, textures, morphs, etc.- then people who decide to reorganize their preset libraries suddenly find all of their reorganized content broken. And unless they're a techie or forum goer, they probably won't know why. They might just stop using that content and buying from either you as a vendor or the entire brokerage.
I've placed a ticket with SM about this before, and been officially blown off. I thought that since they keep saying they want people to use their figures they'd make it so that their stuff didn't break the moment you decided to rename or move a preset folder, but no dice. Every time I get a new version of Poser, I organize the SM content in one central runtime of Poser native content. Then I have to spend about least 2 or 3 hours fixing native content and its references so it can load at all.
Not to mention, other developers can't count on those files being in the same place. I can't speak for others, but that discourages me from making add-ons that need them. That's why I keep my morphs outside of the library folder. I have several very distinct characters I want to make. I'm really hoping I can make morphs good enough that they're useful to others. And I would love to be able to incorporate others' morphs (via references, of course). But I won't distribute a morph preset that references a file that only has a slim chance of actually being there. Not when so many have said so much about the importance of library flexibility as a feature.
The only benefit to putting files in the same folder as the presets is that it's easier to delete the whole item. Maybe I'm totally off in this, but I think most people just leave stuff around, even if they haven't used it in ages.
If you do leave the file in the presets library, then it could be really helpful to edit your cr2 or pp2 anyway, so that you make the link relative instead of absolute. That is to say, instead of ":Runtime:Libraries:Characters:ArtistName:FigureName:file.ext", it should just be "file.ext." That way, if someone decides, say, to put the character in Libraries > Characters > FigureName, or even Libraries > Characters > CharacterType (women, men, birds, etc.), your figure shows up, has its morphs work, and doesn't trigger any error messages. I've had to fix a whole lot of files to make morphs work properly because I changed one folder in my library. And at least I knew what the problem was and how to fix it. To a newbie, all that would have happened was the morphs seemed to load but none of them worked.