Streetlights affect how you plan a safe road journey at night - another thing Google Maps cannot do. Recently, Transport for London has removed the lights from the Hammersmith Flyover (A4) and parts of the Westway (A40), and this means that drivers need to take extra care at night.
Mapping the streetlights on London’s roads is one of OpenStreetMap’s aims, and recently I have added relevant data for many London roads, including the A4 and the aforementioned sections that TfL have removed the streetlights.
Did you know that you can drive from London to Newbury using only roads with streetlights? You obviously cannot use the M4 (unlit between Junctions 8/9-10 and 12-13), but the A4 instead (except for the detour to avoid the Hammersmith flyover).
Addendum: I should also point out that you can also drive to Southend using only roads with streetlights, by following the A13.
Addendum II: I should also also point out that most of my data came from driving trips over the last two years, as well as recent public transport trips within the M25. I respect the privacy of the drivers given the current problems with cyber-bullying on the internet, but thanks.