why to use serializable with java bean

1/*
2One good reason, with respect to servlets, is that if you put 
3serializable beans into your web server session, your web server can 
4serialize them to disk if it's shutting down, and then deserialize them 
5back into memory when it starts up. In this way, users wouldn't lose 
6their sessions / logins when the server comes back up.
7  
8If there are any non-serializable beans in session, tomcat will fail to 
9serialize sessions to disk.
10I believe it's also necessary if you want to sync sessions between 
11multiple servers in a cluster.
12*/