@donovaly, you are right that it is not inherently wrong to add addresses to POIs. The concern is more about the consequences for data maintenance. Once address data is duplicated, future mappers need to keep it consistent - and in practice, this often doesn’t happen. For example, if a notary moves to another location, the node might be moved, but in many cases the address tags remain unchanged, which leads to errors. I still happen to find such cases from 6-7 years ago...

Another side effect is that it can hide the StreetComplete address quest for the building. If a POI carries the address, but the building does not, a new building might never get its address quest shown. That leaves gaps in coverage.

QA tools can help detect such inconsistencies, but it still means additional work for other mappers to investigate and correct them. From a database perspective, duplication is usually avoided in favour of relationships: here, the relationship is "POI X is located in building Y, which has the address". That ensures one reliable source of truth for the address.

That said, adding the address directly to the POI makes sense when it genuinely differs from the building’s address. In those cases, the information is valuable and necessary.

In short, the KISS principle (https://en.wikipedia.org/wiki/KISS_principle) applies here (and not only here).

P.S. Whether a business uses a PO box for its mail is an operational detail of that business and, as far as I know, not something OSM typically records. You can of course tag their ЕИК, which points to our trade register. Anyone who needs this info can go directly to their page on the trade register and see their mailing/HQ address.