Master layers......outline preview....

[morphonius_821]

http://fc36.deviantart.com/fs44/f/20...phonius821.jpg
It depends on what type of stuff people are doing..............
The more complex a design gets, the more cluttered and complex it becomes the more necessary it comes for some people to rely on layers to manage the object load...

And this feature would allow the user to quickly identify all the objects on a certain layer (even if obscured) without having to perhaps go down and switch 9 layers off and back on again.