We really need it as a debugging facility. ATM it's often almost impossible to figure out for how to do something with UNO unless someone already did it, and left a description on the Internet. E.g. suppose one needs to change a style of the first page of a writer document — it is the property «PageDescName» of the first paragraph. And it's just impossible to infer deductively (why paragraph? One would imagine it is e.g. TextCursor, but a paragraph could easily span for multiple pages). So, if UNO state saving would be possible, one could easily write a state to a file, make a change they're interested in, and save it again. And by looking at the difference between the files it is easy to figure out which properties just changed.
One learns about the ways of the API by reading the fine documentation in the form of the DevGuide, or the IDL reference: https://wiki.openoffice.org/wiki/Documentation/DevGuide/Text/Formatting Or by using nice tools like XRay. http://bernard.marcelly.perso.sfr.fr/Files_en/XrayTool60_en.odt We're not going to implement a generic process state dumping mechanism.
I guess this is meanwhile covered satisfactorily by the mail thread starting at <http://listarchives.libreoffice.org/global/users/msg45771.html> "[libreoffice-users] Re: Save UNO state?"