Do you need a project management system if you work alone? I mean a project management system that includes issue tracking, wiki, etc. Currently I keep my issues in a very good organizer software and I keep project documentation in Word files (and of course I have a version control system), so I am not really sure if I need a project management software, because I work alone.
One useful thing, I can think of, that project management system can additionally give me is linking issues with commits (UPDATE: I've found this feature useful enough: for example, right now I am creating documentation for the new release of my project and I consequently open every issue with "Pending for release" status, then I read the issue's description and then I can quickly view the diff of the commit for this issue - this helps me to see details and write better documentation).
Another one - sharing issues so your users or your employer can view or manage them.
What am I missing? Is project management software necessary when working as the only programmer?
UPDATE: I've thought up another useful thing: In comments we can give a link to an issue or a wiki article with detailed information about the code being commented.