Essentially you're giving away a lot more info about yourself than you might realise. If someone who takes an unfriendly interest in you wants to, they can probably find out a lot more info about your habits, likes, dislikes, interests, political views, waking hours, etc than just what you've publicly commented!
Never pay for an inferior experience, but for £2.50 a month the experience of using Spotify instead of having to manually find, download, synchronise, and manage a music library is worth it for me.
Essentially you're giving away a lot more info about yourself than you might realise. If someone who takes an unfriendly interest in you wants to, they can probably find out a lot more info about your habits, likes, dislikes, interests, political views, waking hours, etc than just what you've publicly commented!