I'm not so sure. If I load a saved map in Google Maps (e.g. someone has saved a route with markers and shared it with me), and then I go offline whilst viewing it, Google Maps on Android will show an error after a while and I'll lose the route and markers entirely. This occurs even if I've marked the area as an offline map. I guess it's just a case that they treat the saved routes in a different way. But it's really annoying for my use case (which is finding crewing points for long distance running events in the middle of nowhere with no mobile coverage).

I was talking about Google Maps on iOS. There are countless instances where it will refuse to work without a connection; there's even a modal pop-up to scold you for not having a connection, rather than trigger a dedicated mode like other Google apps. You can't lock in a destination and have the routing work consistently until you are there. The journey will disappear at some point without a warning. You can't find it back without an active connection. Simply having the option to lock a journey and only delete it when expressly told so would be a major improvement.

Sure you can download local maps. but that just saves some bandwidth. Neither Search nor Routing works offline. Without Routing, the app loses most of its uses. Not having Search wouldn't be a problem if you could pick a location on a map and ask: what's there? or even flag it––but you can't. You have to find the name otherwise and search for that, often zooming ridiculously close to get the location you are interested in to appear.