Security
Java Web Start uses security of the Java platform. Users should not be worried about the security model because a Java Web Start application is restricted to a sandbox and cannot corrupt user’s systems. If the application provides additional security (signed JAR files), , then the user has to decide if he trusts the application’s source and, if so, allow it to run. Nothing can happen behind the scenes without the user’s awareness and approval. So its safe.

Performance
Applications launched with Java Web Start are cached locally, for improved performance.

Familiar Java development requirements
Applications developed to run with Java Web Start are developed in the same way as ordinary Java applications. You just have to take care of packaging requirements. Another good thing is that updating a legacy application to be deployed through Java Web Start is, in most cases, a simple process.