Reading the microsoft documentation http://msdn.microsoft.com/en-us/library/bb738684.aspx I see they explicitly open and close the connection
using (EntityCo
It is not necessary because Dispose invoked by using statement will handle it. But it is good habit to explicitly call Close once you know that connection will not be needed any more. For example you don't know how complex the disposal is so you want to free database connection wrapped by entity connection as soon as possible.