I think any scientist should able to convey at least the high level concepts that they're working on at the level that a smart 12th-grader can follow. If you can't do that, I think that's a sign that you're probably not thinking about your work very clearly. Being able to distill things and context-switch back to a birds-eye view of your work is critical for knowing what direction you're heading in.

(I say this from the perspective of a climate scientist - our field has a pretty active public/lay conversation and lots of science comma, but I think the concept still applies to other sciences, and social sciences.)