SQL Server usually chooses the correct type of lock and the lock mode. You should override this behavior only if thorough testing has shown that a different approach is preferable. Keep in mind that setting an isolation level affects the locks that held, the conflicts that cause blocking, and the duration of your locks. Your isolation level is in effect for an entire session, and you should choose the one that provides the data consistency required by your application. Use table-level locking hints to change the default locking behavior only when necessary. Disallowing a locking level can adversely affect concurrency.
T-SQL syntax allows you to specify locking hints for individual tables when they are referenced in ...