Technically speaking, comments should be used for planning and reviewing, code description, algorithmic description, resource inclusion or debugging. Often times comments serve as nothing more than a digital notepad and this use of comments should be avoided.
What’s the harm?
Whether a comment or not, everything in a file takes up space and does stuff. Whether concerned about page speed or possible errors, the thoughtful use of comments makes a difference. Commenting out code does not equate deleting code, and many programs read and potentially render the comments. If you do not need the code, then delete it.
Third party reviews of code often site poor commenting as a reason to dump a development firm. A comment which describes the formula used to create a validation can ease bypassing the validation. Unprofessional comments are occasionally seen over the shoulder by clients. Search engines are reading and judging your comments, and no one wants to anger the search engine giants.
Comment with care
Venting frustrations makes you feel better, but doesn’t fix anything. Hilarious comments make the code funnier, but not better. Thoughtful use of comments makes the code better.