Standard security is the maximum security option for SQL Server. If you implemented SQL Server standard security, you must enter a user account and a password to connect to a SQL Server database. If you selected the SMS Express Setup option, the sa account is used to access the database. If you used the Custom Setup option, SMS Setup prompted you to specify the account you want to use when the system accesses SQL Server (by default, the sa account). No other accounts are necessary, because WBEM security controls access to the SMS site database.
Specify a New SQL Server Account
About Integrated Security in SQL Server
About the SQL Server Account
SMS Accounts Configuration Overview