I started using it because it allows you to download huge areas as vector maps for offline use. But I find myself slowly using it more and more. The only things missing that keep me using gmaps are search, reviews / places, and directions that factor traffic (not a biggie tbh). However, I've been playing with mapbox and, without any prior experience whatsoever got a traffic overlay working within a few hours with a free account. I believe they provide the other parts (search, routing & places) too, I just need to figure out how to plumb them in.
I have tried a ton of map apps and IMO OSMAnd has all the pieces to be a serious competitior, at least for technical folks, with just a little bit of commercialization... The gmaps moat is not as deep or as wide as it seems.
If you are an OSMAnd dev reading this, I will happily pay a monthly fee for this stuff if provided as a cost plus package... I get a ton of value out of the app already, already pay for it and hate Google maps more with every passing day.