I agree with the spirit of this "rule", but sometimes I leave in deprecated code, but for a different reason. I leave it there because I'm afraid I (or someone else) will come back in the future and think it is a good solution to an issue. So I leave in the code with a comment that it doesn't work. It saves me (them) from trying it out only to discover that it doesn't work. Or, worse, from trying it out and not realizing that it doesn't work because they don't test on the case where it fails. (Better solution: Add the case to the module's test code. LOL! As if I write test code!)