Google Maps for mobile devices fundamentally fails because mobile data coverage is far from ubiquitous or reliable for something that important.
The only slight downside is there is a limit to how big a single downloaded map can be. So if you want to download all of Europe you have download it as a whole bunch of smaller maps and switch between them rather than a single big map, but realistically I've never run into problems with the size limitation
If you have the offline map, you can still do this even if you can't use the GPS navigation feature.
I can make coffee by pounding my own grinds and boiling water over a campfire. But if I wake up expecting to turn the coffee maker on and can't, it can throw off my day. Further Google Maps is a terrible, terrible way to handle navigate on a smartphone, especially in a dense urban area with layers of highways.