Chris Shaw talks about auto-shrink:
If you are new to being a Database Administrator or the Primary focus of your job is not to be a DBA you may see the benefits of shrinking a database automatically. If the database shrinks by itself, it might be considered self-management; however, there is a problem when doing this.
When you shrink a data file SQL Server goes in and recovers all the unused pages, during the process it is giving that space back to the OS so the space can be used somewhere else. The downstream effect of this is going to be the fact your indexes are going to become fragmented. This can be demonstrated in a simple test.
Friends don’t let friends auto-shrink.