Checking out the 3.0 preview. While it is extremely useful to be able to create sub-tasks, we need the ability to re-group issues later on. Some use cases:

• It happens all the time that someone creates an issue which is later on found to be part of a larger one. No one knows every issue and finds a suitable parent right away.
• Or we decide to restructure issues later on.
• Or we migrate from 2.6, where we have defined a link type "Sub-Issue", as probably 90% of all Jira installations have; at least we want to manually convert this link type to the sub-task concept (as Lars Kühne posted on jira-users).