What are the main advantages of ORM like hibernate?

Hibernate implements extremely high-concurrency architecture with no resource-contention issues. This architecture scales extremely well as concurrency increases in a cluster or on a single machine.
Other performance related optimizations that hibernate performs are:

• Caching objects
• Executing SQL statements later, when needed
• Never updating unmodified objects
• Efficient Collection Handling
• Rolling two updates into one
• Updating only the modified columns
• Outer join fetching
• Lazy collection initialization
• Lazy object initialization