To precompile or not to precompile.... It depends on what you are doing.
When I am working on a small "experimental" webapp - just playing around with things, then I let the server do the compile because it is easier and more productive.
But on projects where there is a large webapp, I like to build it with the rest of the source code. That is what we have here, after all - source code.
The advantage to compiling at build time is you will find things that might be broken - if you let the server do it, then you have to browse to every single page before you find out if its good or not.
Compiling won't tell you if it actually works, but it is a first step.
For webapps that I am checking in to source control, I like to make sure it builds - so I use weblogic.jspc on these. So if I change an EJB, for example, I can rerun a clean build and make sure I didn't break some JSP that calls that EJB.
Ant does have tasks for doing weblogic jspc, but I usually use a <
java classname="weblogic.jspc" ... /> task because I like to know exactly what options I am setting (where's the :controlfreak: graemlin?). Also I tend to be working one WebLogic version ahead of ant, so sometimes this stuff doesn't work for me. If the ant tasks do the job for you, use 'em.