There's almost no "always" in coding :) If you know enough about the reasons behind codinga guideline and have really good reason for breaking it, then do so.
For instance I comment out code when I do "kamikaze-refactoring" and need a visual reminder to add things back or remember how the old code worked for a while. It's crucial in instances like this that you'll delete the comments later on though otherwise they'll simply clutter your code.