Yann works for a "personalized retargeting company" and knows stuff better than I do.
GeoIP -> Pertinence and truth that is quite relative. Usually the ISP End points rather than the users.
More indicative than anything else.
MaxMind usually more used to understand traffic (from server side), to find out where people come from and which server to redirect them to (if you have different servers).
Personalizing content (language).
In advertising it is used for redirecting towards the country based adverts. Also used to identify threats in case of attacks (to see if they always come from the same source for stats), even though most attackers try to mask their identity, it can still be interesting.
Geolocation databases gives a rough idea and are useful but that is all.
Also there isnt any good Ipv6 Geo database yet and it would be complicated to make one. (they're not necessary given in blocks)
For phones we use GPS and Wi-Fi (triangulation). It's more efficient (calculating distances between known points).
GeoIP location might become the least used method although the easiest to use (information is not precise enough for tracking people)