Today I used 1/4 of my cell data without realizing, and this is not the first time I notice until it's too late. I use Spotify every single day, and on most of them I'm going in and out of my home several times a day.
The only reason I use the "Offline Mode" toggle is because I don't have an unlimited data plan or unlimited money, so every MB counts.
What I really would love to have is the option to toggle cell data use. Either by blocking all cel data use across the app, or just avoiding to use it for streaming. That way we wouldn't have to remeber to enable and disable offline mode everyday (as in my case). I personally would have cell data blocking always on, and never use offline mode again.