JSP precompile issue - moving to JRE 1.5

We are in the process of migrating our app which is based on JDK 1.4.2 and runs on JRE 1.4.2. We will now be switchin to JRE 1.5._06 and I am told that we need to precompile all the JSPs -- i'm not sure why this is required shouldnt this be taken care of when the app gets deployed and the page is called .. why do i need to precompile i'm just trying to understand.. any help is appreciated .... RR

[408 byte] By [safaqa] at [2007-10-2 23:56:46]