Comments are designed to be temporary clarifications about specific questions/answers and as such are cleared at regular intervals. 

As the [Comments privilege page mentions](http://superuser.com/help/privileges/comment)

> - Comments are **temporary** "Post-It" notes left on a question or answer. 

> Comments are not recommended for any of the following:

> - Suggesting corrections that don't fundamentally change the meaning of the post; instead, make or suggest an edit;

> - Answering a question or providing an alternate solution to an existing answer; instead, post an actual answer (or edit to expand an existing one);

> - Compliments which do not add new information ("+1, great answer!"); instead, up-vote it and pay it forward;

> - Criticisms which do not add anything constructive ("-1, see previous comments you scallywag!"); instead, down-vote (and provide or up-vote a better answer if appropriate);

> - Secondary discussion or debating a controversial point; please use chat instead;

> - Discussion of community behavior or site policies; please use meta instead.