It's not unusual for running programs to write data to your hard drive. Say, saving a configuration file or committing to a database. A few megabytes never hurt anybody. But tens of gigabytes an hour? Up until recently, the Spotify client was wreaking this sort of data-based havoc, though a patch has supposedly solved the problem.
A few weeks ago, a Spotify user by the handle "MinionMan74" reported that the Windows client was writing absurd amounts of data to their hard drive. It didn't take long for other users to come out of the woodwork with similar issues.
For instance, user "koutasn" tracked Spotify writing 10GB an hour to their poor SSD, while another named "firef" recorded some 100GB committed in a single day.
So what, you might ask? Well, if you have an SSD with a limited write count, you're not doing it any favours. Sure, it might be a while before you noticed anything, but that sort of throughput could shave years off your drive's lifespan.
In the same thread, a Spotify representative states that an update has been released to fix the problem:
We've seen some questions in our Community around the amount of written data using the Spotify client on desktop. These have been reviewed and any potential concerns have now been addressed in version 1.0.42, currently rolling out to all users.
Although it's brought relief to some users, others in that thread continue to report ridiculous write amounts. Still, it can't hurt to update Spotify right now -- your SSD will thank you.