Detail mesh pipeline

Can anyone point me to a breakdown of the detail mesh pipeline? What’s accepted what’s not etc. The documentation is lacking to say the least. Some meshes draw OK while others will not paint on the surface at all.

Are there material constraints? Mesh constraints?

Is there anyway to randomly rotate objects like rocks etc?

Really feels like this system is lacking significant features that developers would want in there pipeline.

FYI using unity 5.6.3

Honestly other that rocks is there a decent use case for other detail objects like shrubs etc? Or should basically everything other than billboard grass and vertex lit rocks be instanced as trees?