late penalties

Anyone want to take a break from political news and reflect on grading policies? Specifically, what penalties are appropriate for late papers and exercises? In practice, these range from the extremely Draconian “no late work accepted at all, you just get a zero” to the extremely lax “whenever” and include a huge middle ground of grade reductions and policies about which excuses for lateness are justified or not.

My own policies are not entirely consistent but tend to the middle ground: I think students should get more credit for doing work than for not doing it, even if it is late, but that there should be penalties for lateness that are proportional to the academic harm done (or advantage gained).