I think it's a good idea too.
Other sites often allow for this via a person's profile.
It's up to individuals whether they actually give this or indeed any profile info at all. information, but if they do, their location is often shown below their name.
One of the sites that I use is a language forum, where the country (and sometimes the region) of a poster is displayed, and another is a uk gardening forum, where a poster's region is shown, assuming they gave that info.
On both of those forums, it is really useful info to know when giving or receiving advice, and I agree that there are often posts on Gransnet where it would be equally useful to know at a glance in which country or region the poster is living.