In combination with downloadable map tiles, I can plan and ride my route completely offline which saves battery and keeps things running in the more rural areas.
The route planner is really nice. I actually plan all my routes in the smartphone and export to gpx if necessary because it's the most comfortable way to do it.
What I also really appreciate is, that it's not a subscription based payment model. So you pay once for downloadable tiles etc. and for the app and can just use it without worrying about updated terms etc.
BUT, and that's a major BUT, the version is deprecated and will be ended soon in favour of the subscription based locus map 4. I don't miss anything in locus map 3 and don't see any benefits. I'll just hope the app will work as long as possible without official support.