Login As allows admin users to login as other users in the system.

This plugin is not meant to help you spy on your users.

The purpose of this plugin is to fill a gap in Elgg's admin features
and help admins maintain a quality site by performing some actions 
as a different user.  For example, if a user flags a message in his
internal mailbox, there is no easy way for the admin user to view
that message.

This plugin is also to help troubleshoot user-specific bugs.  Sometimes
it's easier to see exactly what the user is seeing when troubleshooting.

Once logged in as a user, everything you do will show up like you are that user.

Be careful.