How does LyX's branches feature work?

[Uwe Stöhr]

I'm currently revising the Userguide and stumbled over the Branches feature:
In the document settings you can set and manage branches of your document but I 
don't get them to work.
Branches are not yet described in the docs yet, so if anybody could describe me shortly how it 
works, I'll add this to the LyX docs.

thanks in advance and regards
Uwe