Developers will love this latest improvement, specially those that have SQL Server Express installed on their laptops or workstations but still work with full versions of SQL Server on their network.
In the past you have to have at least the Developer Version of SQL Server if you also wanted to have the complete features of SQL Server Management Studio.
Thanks to SQL Server 2012 SP1:
SSMS Complete in Express
Customers who use the SQL Server Express With Tools, SQL Server Express COMP, SQL Server Express with Advanced Services and SQL Server Management Studio Express now have SQL Server Management Studio complete. These Express Editions now ship the SSMS feature with functionalities that exist with the SSMS from full editions of SQL Server.
– MSDN Library
More info on What’s New in SQL Server 2012 SP1 here