Inevitably, it's used in situations such as "as I have clearly said".
Firstly, we are none of us best-placed to judge the clarity of our own language use to others.
Secondly, if you have to tell other people you were being clear, you're being condescending. It's telling them they're too stupid or inattentive to have realized on their own how effective your communication was.
Until now, I'd never realized how insulting nominal clarity could be.