As the title details, the property window for each object selected will also list all the layouts that the object presently has at least one instance thereof.
So if you have three layouts (LO_1, LO_2, and LO_3) and Object_A exists on both LO_1 and LO_2 then the properties window for Object_A will list those two layouts.
As an extra level of detailed info, each layout listing could include the number of instances on that layout.
The benefit here is that it will help the developer to locate where certain objects exist, if any, and can help with editing when the project gets particularly large, as many projects can easily reach a huge number of layouts.
This could be the layout version of the Event Finder (Ctrl+F) on event sheets.