Spotify is $10 / month, the price of one album. For that, I get an essentially infinite [1] library of music that's basically always available to me whenever I want, curated playlists, discovery features, sharing features [2], etc, etc. It all just works, I never have to think about it, etc.
By contrast, unless I'm pirating music, what does $10 get me? An album a month? So after a year, I own 12 albums and had to hassle with the files and downloads, whereas with Spotify it just works and I've listened to 10x - 100x that much music.
Yes, if / when I stop paying for Spotify, I'll lose access, but so what? I wasn't planning on spending 20 years paying a fortune to accumulate a music library and then stopping cold and never paying again, just listening to that music I bought. I'm happy to just pay $50 - 100 / month until I die for subscriptions to huge and ever-growing libraries of music, movies, TV shows, books, etc. Seems like a fantastic deal.
1. I don't have niche tastes or a deep attachment to any particular artist that I simply MUST have, so their selection is far beyond anything I really need.
2. I don't use these, but still.
I signed up for an insane promo with Sprint in December where we switched from Verizon and got 13 months of unlimited everything (except 4G tethering, I think that's capped at 10gb per month) for free.
Honestly though, we don't use all that much bandwidth anyway. I'm usually on wifi and for the times that I'm not going to be, my playlists and podcasts download in the background when I am.
Spotify is great. I can listen to charts/viral music from different countries. I can usually find music from other countries as well if I need to.