In some projects JIRA issues may be large, complicated and have a long life. In such an issue you may need to review last comments to recall its context.
Using Personal Notes add-on you can store the "next step" that you need to do to move the issue.
Then you can see issues with personal notes in issue list. This way you can grasp context of each issue quickly and see the whole situation easily.
Your "next step" may be noticeable for you but absolutely useless for others, that's why it's private. If your note is important for others, it's better to use comment to share it.
Add your private note on issue page
Add column to issue navigator. The column displays text of note and issue summary.
Private notes content is available for search in advanced mode.