By the time you get to the drawing level in Pro/e, you've crammed part, assembly, component and drawing layers into the layer tree. Even assuming you have all those layers blanked, they require a lot of overhead. Seems like I spent half a day not too long ago trying to unblank particular datam layers, only to find that every time I clicked on the layer name, it would red highlight a thousand datums or coordinate systems while I waited helplessly for it to finish (minutes later). Well, I finally figured out how to prevent this drain on the overhead. In the layer tree Settings tab, uncheck Layer Items. No more highlighting of every item on the layer and changing layer status is a snap, especially useful on large assemblies.
David Janes