Just keep in mind, they're not optified, being meant for the SDK scratchbox environment, rather than the devices directly, so you have to manually optify them if you want to save some rootfs space.

I have scripts that automatically move all the significantly-sized files from them if you'd like. (although I think I have the standard 'include' directory symlinked to /opt by default as part of a different, stuff-that's-on-the-N900-by-default optification script)