Case for separate module URLs:

USE CASE

Traffic analysis of your site shows that most visitors
require module A (big, almost never changes) and only
a few visitors require module B (small, changes often).

Keep those modules at separate URLs and everyone will
only download module A rarely. On subsequent pages/visits
that data will come straight from user-agent's cache.

Combine them into a single URL and everyone will have
to download modules A+B every single time module B
changes, even though most visitors never even use B.