Functional modeling in design practice?

This is a question mainly for professional engineering designers. I'm interested in assessing the extent to which product designers use
functional modeling methodologies (like those described by Pahl and Beitz, et al) in their design projects. I'm also interested in knowing if you know of other applications of functional modeling (ie, not direct personal experience), or even if you've never heard of it. If you have used it, did you find it worthwhile?
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