Locking is about protecting the integrity of your data. Sometimes you need to be sure that only one user can update critical data at one time. Sometimes, access to sensitive objects in your system need to be serialized so that data is not corrupted by concurrent reads and writes. Databases traditionally provide this sort of functionality with transactional scopes and table and row locking facilities.

Entity beans are a great way to provide an object-oriented interface to relational data. Beyond that, they can improve performance by taking the load off of the database through caching and delaying updates until absolutely needed so that the database efficiency can be maximized. But, with caching, data integrity is a problem, so some form of application server level locking is needed for entity beans to provide the transaction isolation properties that you are used to with traditional databases.