SU for Bamboo provides administrators with the ability to take on the identity of users for testing, access validation and setup.
A small modification to a template file is required to add the 'SU' link shown on the banner. The wiki, linked via the Configuration screen of the plugin, has all the details.
An administrator can remain in the users role indefinitely, there is an SU-Exit link on the user Dashboard, allowing quick reversal of roles. For security, this link is present for 5 minutes only.