Consider a detached house with a detached garage on a plot of land clearly de-marking the house from its surroundings. What tags should be added to the garage? The house has its associated address tags. I can think of three options and I am interested in the pros and cons of each, as well as which is recommended (or more options if relevant):
My practice has been to put the address on the house and leave the garage un-addressed. My reason being that for navigation it is much more likely that the desired destination is the house.
There are some QA tools that see duplicated addresses as an issue to be fixed. So if you put the address on both the garage and the house they will be flagged as errors for someone to go and fix.
I see no particular reason to create a relationship containing the house and garage.
There are some rural areas where it is hard to determine the main building that may be desired for a destination, in those I use a node with the address in what looks like an appropriate place near the buildings.
For a commercial situation, there are many gasoline/petrol stations where there is an overhead canopy (building=roof) over the gas pumps and a separate building (“building=retail”) housing a convenience store. The store and the fuel having separate branding or naming but both sharing the same address. In those cases I will draw a “landuse=retail” area around the whole of the property and put the address on it. Then I separately tag the buildings for name, shop, amenity, etc.