A skeleton part has a similar goal as working in-context does, i.e. parts are not their own little island, but one part knows about its neighbour and can react to how it updates. This can make design changes much quicker and less painful.
Ok. with that out of the way, next question: why not just use in-context?
In-context makes links, one part references another, right? well if you do that for a few parts, it's already hard to really track what's going on right? what is tied to what, and how? By using a skeleton part you know all the links are funneled to and through the skeleton part.
For sure it's an old Pro|E term, this technique has been employed practically since its birth in the early '90s. Way before my time, that's for sure!
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