Simple Calendar Pro, Aegis, Feeder, and NewPipe are a few examples of open source apps available through F-Droid that allow you to easily export your data.
When you sporadically decide to back your stuff up it might be a good idea to include them with everything else.
You can also use these files to transfer data between apps. If you are using Feeder as an RSS reader on your phone you can transfer the OPML file to GFeeds on your computer.
My big push was de-googling my phone (and being unaware of Aurora store at the time). It was frustrating not being able to easily use my 2FA codes and listen to my usual podcasts because Spotify wasn’t available as a simple APK from the website.