Greetings! According to the OSM Wiki - which is what I try to go by when deciding how to tag things, tagging single nodes with building=house is acceptable (https://wiki.openstreetmap.org/wiki/Tag:building%3Dhouse). There are several ways this data can be useful, even though it does not currently render on openstreetmap.org. Personally, I want to be able to figure out if a wireless internet service provider tower were built at some location, how many potential customers (houses) could it see? There are a lot of houses to add, and I don't have much free time, so Ctrl-V is much faster than 3 clicks and then also editing a tag. Additionally, single node houses *are* actually rendered if they have an addr:housenumber tag, like these: https://www.openstreetmap.org/#map=18/33.42251/-84.69122. As I have time, I want to add housenumber tags to these nodes, in order to increase the accuracy of tools like Nominatim - in which case they would be useful even if they were never rendered on any map at all.
If someone would like to draw rectangles for each house, it's not too difficult to upgrade these from a point to a polygon by copying the node and then "Paste Tags" (Ctrl-Shift-V) onto the new rectangle, and then deleting the original node, but I personally don't have time to do so at the moment. Also, the way that openstreetmap currently renders these nodes is not necessarily the way that it will always render them - perhaps someday single-node houses will be rendered on the map. It's nice to meet you! Happy mapping! lightning/Daniel