I'm using it to gather crash information only. I am not using it for any other purpose.
The history here is I've been using Crashlytics for personal projects since forever. Crashlytics used to be part of Fabric which was bought by Twitter. It was then sold to Google. I've never felt a reason to change it so I just use it by default for all of my apps.
Crashlytics: https://firebase.google.com/docs/crashlytics