I posted about this in the forums in June but forgot to post here:
Windows system resources percentage goes down upon the opening of each new layer but does not go back up when closing that layer. So during the course of a browsing session, having opened and closed many layers, but now just viewing 1 open layer, the system resources can be below 10%. This is not the case with new KM windows. The percentage does go back up when closing a window.
My completely uneducated guess is that closing each layer doesn't actually close it but just hides it until exiting out of KM completely. I don't know if this is assumed behavior from the layer plugin by design, or a design flaw, but it requires the user to exit KM prematurely if multiple layers are continually opened and closed.
Tested using TclockEx on Win98