Never. No.
In contrast. Is there any reason to NOT self-vote? If you are not believing that what you wrote deserves a 100% upvote, why should others do?
The only exception is, if you e.g. just post a question, or the post took 3 minutes to produce. In that case I would restrain from self-voting.
Wow. Again I never thought of it that way. Since I joined I always read the opposite. Then again, This is a big place. Thanks for clearing my confusion.