Well, because you don't want there to be WT parts for every single CAD part. There are often times you may have an instance of a CAD part, for example a flexible brake line. The binned part might just be a "straight" 20" long hose, used in multiple different locations. However, when installed the part takes on a particular shape for routing. This "installed" version of the part will not have an owner link to any WT parts, so I do not want it to auto associate and have one. Another example is when using large assemblies, especially in a structure with optional equipment, you may have many levels of "install" assemblies, where you need the rest of the product shown for locational information and installation procedures, however this assembly does not go into the final product structure, or else you would have duplicate parts in the production model (and/or eBOM) structure.
There are many, many, many reasons why you may want this, which is why PTC has a way for you to do it. I just can't seen to find it.
