I have Poser 11. I am experimenting with a posable breast pocket which is a posable extra jointed part parented to his chest, with its rotation center at its bottom edge. Parts of its edges were not adhering to the garment. That was because the pocket strayed into lCollar and abdomen territory. So I added two extra weld commands to the testing job's .pz3 file :-

    weld    lToe:1  
             lFoot:1
    weld    pocket:1  
             chest:1
    weld    pocket:1  
             lCollar:1
    weld    pocket:1  
             abdomen:1
    allowsBending 1 

That seems to work, but is it likely to cause other trouble?

No doubt it will but no idea which problems you wil run into. Interesting experiment. Looking forward to hear your furthrer findings.

Wardrobe Wizard has used additional weld commands for years. I doubt if anyone has noticed although they would have if the commands were not there.

Some forms of non-standard welding were broken by changes introduced with the alternate skinning methods. These can be re-enabled by checking Figure-->Properties-->Enable Legacy Welding. Other than that, Poser has remained tolerant of extra or unusual welds.

Just imagining for a sec a pocket and the underlying shirt, welding verts together there would result in non-manifold geometry with three faces sharing the same edge.

https://knowledge.autodesk.com/support/maya-lt/learn-explore/caas/CloudHelp/cloudhelp/2015/ENU/MayaLT/files/Polygons-overview-Twomanifold-vs--nonmanifold-polygonal-geometry-htm.html

That's A Bad Thing ™ in normal 3D modeling. If Poser doesn't care, though, then I guess you shouldn't. A solution that didn't involve that would likely be using a weight map instead of a standard Poser deformer, so you could fine-tune the rigging to not move the verts at the edges of the pocket.