Thank you for your responds and the further information.
The Idea behind the proxies is, that when using it as a present in an other scene,
I don´t want to have the geometrie loaded inside that scene. I also do that in ForestPack.
Unfortunatly mostly afterwards, but it is a huge timesaver..
The original file is smaller, quicker to autosave and quicker to send into the local renderfarm.
Especially for trees, cars, people in archictureal renderings, there is most of the time no need to keep the geometrie in the scene.
Thats why I try to use proxies.