Thats fine however the reason I tried to clarrify is I want to know the answer to this too and you might also in the future and so might someone else who comes across this post.
So the kind of scenario I think you are asking is that on every page/folder/news item in the news section you want a special "latest news items" box for example. But not in other parts of the site. But you also want to include navigation and slider and other elements from your default site layout which the rest of the site has, without having to update those in two places.
The way I think it works is that it doesn't use inheriting tiles and slots like portlets does. Instead you create several layouts. The layouts contain the tiles. So you would go set the layout on all the subcontent and perhaps there is a way have a content inherit it's choice of layout from it's parent?
ie, a mosaic page is a merge between the globally defined layout and the current content, and not merging in stuff from parents (unless a specific tile does that internally). Tiles "live" in the content item or the layout, and don't get reused anywhere else.
@datakurre @tkimnguyen Am I on the right track? Clarity on this would be very useful.