From Meta Stack Exchange, How do comments work?:
... . Comments are often used to ask for clarification on, suggest corrections to, and provide meta-information about posts. ... .
Usually, users who post lots of comments in the scope of above sentence are doing a great job by helping OPs improve their posts. On the other, frequently commenting means there will be a long tail of comments in those user's history if such comments are not latter deleted, which is what happens in many occasions:
In reality, many obsolete or chatty comments remain untouched due to the high volume of comments posted ...
What are the downsides of not deleting our own comments (specially the obsolete ones) in relation to how we maintain GIS SE and/or in relation to how we expect to keep the highest signal-to-noise ratio as possible?
Right now, I am more interested to know if there are disadvantages of keeping a long track of comments (i.e., not deleting them), rather than to discuss if such disadvantages (if they exist) overweight the benefits of commenting to provide feedback to OPs (which again, I consider to be a very important activity).