The main reason I got Spotify Premium was to be able to play music in my car without streaming and thus save money on my data plan. I go hands free and use Google Assistant voice commands. The implementation between the two is very poor. I cannot use Spotify in offline mode with Google Assistant. This creates an issue where I can voice command to play an album that I have downloaded and instead I get something similar streaming, which has often happened. Sometimes I don't realize I'm actually streaming until a few songs in and then have to try numerous voice commands to try and convice Google Assistant to just play from my downloaded albums. It seems the preference is streaming over my downloads, very annoying.
At the very least I should be able to say "Play downloaded album..." or just make Spotify available in offline mode via Google Assistant.