The fact you can add major changes which have occurred around you immediately.

Sometimes you have to wait months, even years to see a major change on a map, such as a new freeway opening. In Melbourne, Australia, our most dangerous and busy railway crossing was recently removed, with the rail line and road shut for 10 days for grade separation. The major works are now completed, and the new station location, new rails and re-opened road with no more level crossing are now present in OpenStreetMap, in preparation for opening day!