Define common defaults
Ideally, the default settings should provide the experience users expect when downloading an app and meet their primary goals. That's why user research is a vital step in the product development process. Design decisions based on your team's experiences or preferences have nothing to do with the needs of end-users.
You may guess and build assumptions about what settings will be right for your users, but it's difficult to be accurate. Eventually, products released without user research turn into junk and cost businesses a lot of time and resources.
Instead, you may find a group of users, conduct a few user interviews, and find out how people expect things to work. For example, if it's a messenger app, consider asking the target audience questions like:
- Do you expect a messenger app to download all shared media with cellular data when Wi-Fi isn't available?
- Do you expect other app users to see your profile photo and the time of your last visit?
- Do you want to share your live location with all your contacts?

