A basic question about red5 server

I am new to red5 and have a very basic question.
I tried some example applications given but there java code for red5 applications is very small as compared to actionscript code required for running that application.Is it same for all real world applications or it's just in case of examples?
What exactly is the role of red5 application?I mean if most of the part is done in actionscript then what part of any project is handled using java code on server side?