JCA was started in 9.0. It represents the entire architecture UI on the
presentation tier of an MVC patterned framework. JSCA is a redevelopment
effort of this where JCA is generated via JavaScript hence "JS" in JSCA.
It's largest usage is in JSCA Tables via the JSTableObject object. It's
used in 9.1 and a lot more in 10 because now that you data more easily
managed in JavaScript based data structures you can do AJAX invocations to
post user interactions back to the servers. Revise/Check In tables are an
example its usage. Unfortunately, many JSTableObjects/JSCA tables are still
created with template processors instead of tag libraries. I haven't dug
deep enough into 10 yet, but I would hope they changed this as they promised
to do away with template processing.