Question of setting dynamic cache service

[mixmouse]

When I read the WAS inforcentre, I found there were two different places I could set up the dynamic cache service, one is on WAS server (through the WAS console to enable the servlet cache for application server), another one is on HTTP server (through the plug-in.xml and install SynaCacheEsi application). Now I am getting confused.

1. Which dynamic cache should I enable? on HTTP server or on WAS server? (My http server and WAS server are on two phsical nodes)
2. What is the advantage and disadvantage for enabling dynamic cache on WAS server?
3. What is the advantage and disadvantage for enabling dynamic cache on HTTP server?
4. If I enable the dynamic cache service on HTTP server and WAS server, what will happen?
5. If I enable the dynamic cache service, does my web page still reflect the database change?

Thanks.