The idea, in my words, is to have a standard on how to link between layers: how to merge them, so to say.

That way, a routing app for a car would only need the roads and their features layers. But the search engine for tourists needs the poi layer and not all the road details.

A 'live' layer for e.g. traffic density could then be a neat commercial product for OSM consumers. But without standards to link your layer to, say, the OSM streets, it is almost impossible to offer and process such a layer.