Eros includes a suite of python scripts, cmake modules, and patches to simplify cross-compilation as well as provide testing for your embedded system.
Its not immediately obvious, but ros/eros can not only provide an environment to cross-compile a full ros platform, but thanks to ros' dependency system and eros' tools, its also a brilliant build environment for managing a large set of cross-compiled, non-ros based packages. Here we refer to this environment as a Partial Cross because it involves compiling the ros core stack natively while cross-compiling your non-ros packages. Time to scale up and take advantage!
Partial Cross : using the ros build tools to assist regular embedded development.
Full Cross : cross compiling everything.
The following notes are not relevant with regards to usage, but provide a better idea of the big picture.
Patches : outlines how and what patches are applied by eros from release to release.