TL;DR: is for more demanding app requirements.
For end-user apps: offline maps support. Google Maps has it as app (and not everywhere), we provide SDK where it works globally. For more demanding needs you can add 3D objects to map, use it for HUD navigation (Google terms prohibit it), use completely own/custom base map etc. See https://www.nutiteq.com/nutiteq-sdk/comparison/ for more more differences and similarities