Why do we need Custom Properties?

OK, so it's a leading question.  I know why we use custom properties, but I'd like some philosophical input as to the best use of SW custom properties in an EPDM environment.

With EPDM, each file can have lots of metadata assigned to it through the variables mechanism.  Variables can be viewed and manipulated through the EPDM interface quite effectively.  They can also be linked to custom properties in the SW files themselves, but I'm beginning to wonder if that practice shouldn't be minimized.

Q:  Under what conditions should a variable be linked to a property in SW as opposed to simply existing as a variable in the EPDM database?

My own thinking is that the only variables that really need to be linked to an SW custom property are those that are actually displayed on a drawing.  You can't do that without mapping the variable to a custom property, but other than that, perhaps there's really no benefit to creating the linked property structure, and dealing with the non-intuitive updating and user changing issues that ensue from them.

Q:  What would be the downside of having no custom properties at all in the SW files, and keeping all pertinent data only as EPDM metadata in variables?

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