Mylyn brings Jira right inside your IDE. You can view your whole list of assigned issues in Jira. If you tell Mylyn which issue your working on, it will remember everything you do in conjunction with that issue. It begins to hide away all the extraneous stuff that does matter right now, allowing you to focus on what does.
What’s more, Mylyn provides the ability to edit and comment on Jira issues right from the IDE, whether you are online or offline. Mylyn handles syncing up any changes you make to Jira when you come back online.