Podcast apps tend to save everything for some stupid reason. My iPhone was full and I noticed Overcast had saved like 3 GB of old episodes. Pretty terrible UX.
Tiny text messages, profile images, avatars, inline linked media, etc.
Start caching the stuff you obviously don't want to re-fetch over HTTP every single time the user scrolls around in their timeline, and 100MB is a pretty reasonable footprint.
If you don't let it finish (say you don't care about that last ad or the outro music and you jump to another episode), it'll keep the file.
Similarly, when you transfer to a new phone or restore, it won't take those files with the backup, and if you have a bunch of files still around, it'll re-download those, taking several hours or days.