Q:

Helpful features for comment

Sometimes in a answer, when OP asks for some moderation of code or discussion about some point of code that given as answer, then we explain that or a give small piece of code through that comment so that OP can understand.
It would be better to give some features in comment section especially code tag, text block/strong/may be italic and bullet list options.
Also, after 5 minutes editing in comment is disabled automatically.So isn't it helpful to extend it? Because conversation in a question and answer may be longer than 5 minutes and editing may need there as per requirement.

A:

The purpose of comments is not to have long-lasting content, nor to really be a troubleshooting session.  Anything that is more complicated than a few sentences should be added as edits to the original question/answer, or as a new answer.  Further, anything of long-term use to future readers should be similarly edited into the question/answer.

A:

Comments are not meant to be long lasting pieces of information; they are transient. Mods will clean up the comments from time to time on a question/answer. Then anything of value that was in there is gone for future users.
If you need to format your comment that much then it is probably valuable and therefore should be a standalone answer or edit to the current answer.

A:

I delete comments often, for the following (not exhaustive!) list of reasons:

The comment thread has turned into a long discussion between two people
The comment thread contains information that is only tangential to the thing being answered
Extended discussion
because it's Tuesday
the comments have devolved into bickering
someone troubleshoots and fixes an entirely separate problem in the comments
because the comments are flagged when they hit a certain length in a certain period of time

If you want the information you post to stick around, put it in an answer. In an answer, you have all those things you want: code formatting, quoting, bulleted and numbered lists, and even the ability for others to coherently comment on what you've written.  These are all things that are difficult (if not impossible) to follow in comments. 

