Agile testing: Exploratory testing vs Automation testing

Automation Testing

• Automated tests are important, but they can't always address the complexity of finding potential problems related to usability, reliability, performance, compatibility and other quality criteria.
• Automated tests can't ensure the documentation matches the final product.
• They don't typically cover test scenarios past common use (like disfavored use or extreme use). 
• Automated tests are great for testing specific aspects of functionality, but for complex applications they aren't so great at testing the platform dependencies (external hardware or software, deployment configurations). 
• They don't often address issues related to operations (dealing with how data ages, alarming/alerting, logging, etc.). 
• And automated tests aren't often focused on relationships between the product and time (concurrency, changing rates or transactions, or delays on input).

Exploratory testing:

• Exploratory testing to help inform the project team about possible issues with the product. 
• Their testing can be unstructured and freestyle
• Exploratory testing is simultaneous learning, test design, and test execution. 
• Exploratory Testing is a Profoundly Situational Practice 

Source- Exploratory testing

                http://searchsoftwarequality.techtarget.com/tip/The-benefits-of-exploratory-testing-in-agile-environments