jetty is for serving your jsp and servlets. If you don't want these, then you will only need apache.
I want to run jsp and servlet. Currently I use jetty for servlet and jsp, and use mod_jk to connect to apache, and planning to move everything to jetty.
However, I don't really sure the benefit I get, so I like to see what advantage can I get if I doing so......
simplicity - you only have one process to configure/manage.
speed - your Http requests will only be handled once. They are currently being deserialised, parsed and reserialised by Apache/mod_jk.