Off the Shelf (listed on the App Store as “Pile: Off the Shelf”) is built to know as little about you as possible. The short version: the app collects no personal data, has no accounts, no analytics, no ads, and no server of its own.
Your pile — the Spotify links you save, their titles, cover-art addresses, and the order you keep them in — is stored locally on your device. If you use iCloud device backups, that local data is included in your device backup like any other app's data. Nothing is stored on our side, because there is no "our side."
To show a title and cover for a link you save, the app calls Spotify's public oEmbed service and loads cover images from Spotify's image servers. These requests go directly from your device to Spotify and contain only the link being looked up — no identity, no account, no advertising identifiers. Like any web request, Spotify's servers see your IP address; those requests are governed by Spotify's privacy policy.
When you play an item, the app hands the link to the Spotify app or your browser, and Spotify takes it from there.
If a future version ever changes any of the above, this policy will be updated and the change described in the App Store release notes before it ships.
Questions? Email anders@lutzhoft.dk.