A number of times I've been building something and had trouble selecting the prim I'm interested in because it is covered by other prims. This tends to happen with any build involving an enclosed space. To work on something inside the camera has to be inside as well in order to select, but then what I'm trying to line up needs the camera to be outside... etc etc.
Really all I want is to be able to temporarily "hide" some objects - "turn off the little layer eye", and the object is gone from the sim, so it doesn't get in the way. When I unhide it it comes back to precisely the right place. Currently I'd have to take parts of the build away some distance and line them up again when I put them back.
There would be some UI issues I guess - one would need a list of the objects you're working on so you could hide/unhide them. Would probably be best to automatically unhide objects soon after the owner has left.