some times after restore database, you find your logins and users mapping is lossed and no user can now logon to database using application. I faced that many times. To map all your database users with master..syslogins. save this procedure in current database and execute it. All users will be mapped with logins.
When doing bulk data changes it may be beneficial to disable indexes prior to starting the operation. Fortunately, SQL's rich metadata makes this very easy to automate in a robust fashion.