This seems a little messy to me but what is the practice for utilizing addresses?
Example:
I say it’s mostly a preference in that some like to use separate address nodes, others add them directly on the building much like how you can have shop as part of a building as well as a node.
Furthermore, apartments as well as semi-detached and terraced houses with no clear separation (or haven’t been separated yet) can have multiple addresses which makes separate address nodes a necessity (well, you can alternatively enter a range but you lose on information that way), though they should be preferably placed on the entrances and not standalone on the building.
Side note
The opposite (i.e. many buildings under one address) like a school complex or business park can also be true, though, and in that case, you have to draw an area with all the address around all the buildings (or use a multipolygon but I don’t like that idea and may in fact be a misuse of tags, especially if two buildings are sharing nodes).
Of course, the commentors on @Herwescheluc also mention that nodes are used when a building has not been drawn which makes address nodes also necessary.
Well, it's more complicated than that
Though that it’s also valid to enter buildings as individual nodes but that is obviously not recommend given that buildings are physical and fairly large objects unlike the nontangible addresses alongside the fact that a lot of information are missed out so it’s only useful to mark a building somewhere but areal images is missing or a building is proposed on this position (IMO the best use-case of building nodes).
Last but not least, you can also enter an interpolated address, essentially the way-equivalent of address nodes and areas by lining them all up on a line which should provide more information than a range of address but still less than individual nodes / individually tagged buildings.
If I see correctly, 
not a single building has been drawn in. Just quickly entered the addresses from another data source! Also a way to live out laziness and still have mapped a lot - good for the mappers own statistics…
