I think you’re right that most groups probably don’t need a full address, not from a practical view anyway, as the events themselves have addresses. Some groups (I guess more likely makerspaces and schools) do have an address that makes sense for the group, but I can’t think of anywhere off the top of my head where it actually needs to be full address for some feature to work.
In the Groups page, if a member has provided their own town/city, we’ll find a list of groups near them based on the lat/long of the member and the lat/long of the group (which comes from the group location that is entered). This would probably still work well in most cases with just the city/county/region principle, although in London it would work better if something more fine-grained than city is used is in the location (e.g. if all groups had simply London as the location, the ordering of the groups wouldn’t help, you might be in South-West London but see a group from North-East first. Of course this also depends on the member having put a borough in their own town/city information, which might not always be the case anyway.)
For the groups near you feature to work best then we’d probably want e.g. ‘Kilburn, London’, ‘Hackney, London’, ‘Brixton, London’ as the location. We could potentially have just ‘Hackney’, ‘Kilburn’, ‘Brixton’ but this leaves the geocoding prone to coming back as some unintended location (often in the US!). We could also have just ‘London’ but with the proviso above that the groups near you might suffer slightly from that.
The map of groups on our site (https://therestartproject.org/groups/) also makes use of the lat/long that comes from the group location, so same thing probably still applies in that we’d want that lat/long to work at a borough/part-of-city level.
I think there probably is value in that, both at a display level on Wordpress, and in terms of geocoding it makes it more likely to be accurate.