Well, when it comes to rigging, where are many ways to skin a cat.

As usual, it depends...

Clothing merchants usually hate JCMs because they are an added complication when transferring a rig from a figure into a piece of clothing. And unless the clothing is really skin tight, you can't just auto-transfer a JCM with a single mouseclick, but you rather have to create a new one for the clothing item that corresponds with the one used in the figure.

Not true, actually.  I can transfer the JCMs to clothing, then edit the morph in place using Poser's existing tools.  A single click to transfer the JCM, then simply edit the JCM in place to make it behave properly in the clothing.  Easy as pie.