It's not only the cliff itself, but threat of the cliff and qualification hysteresis. For some benefits, if it's determined that your categorization changes, then getting accepted into the former level of benefit can take a long time. E.g. if you're told that more than X dollars in your checking account will result in a reduction of benefits, and getting your old status back might take a year, then it's logical to be risk averse and stay well clear of any jobs that could take you over the limit even for a day.