I split disparate business units which will have unique addresses into different buildings -- this is akin to splitting terraced houses.

Most of the centre of Bristol is mapped this way. If you want to combine separate businesses together then I think you need some sort of relation / other container.

Mapping businesses as areas is really simple to explain to beginners -- it let's them be updated really easily. It provides a hierarchy based on size, that can be used by renderers. In contrast having several POIs in a building says nothing about their relative importance / area.

It's possible that something like the simple indoor mapping scheme might capture the best of both -- treating business units as "rooms" -- though unfortunately most renderers don't draw the outlines -- so more difficult to visualize and it's more dificult to explain to beginners.