I have some years of experience with maven projects, even with multi modules ones (which has made me hate the multi modules feature of maven (so the disclaimer is now d
The major benefit of multi modules are
I already worked in a project with about 30 submodules. Sometimes, you need to change something in more than module, and running one single command and being sure that everything that need to be compiled is compiled in the correct order is a must.
EDIT
Why 30 submodules ?
Huge framework with lot's a features, lot's of developers, separation of features on a module base. It's a real life use case and the separation of the code into module was really meaningful.