[2020] I hope Bungie can do some in-game promotion for their "in-house" Destiny 2 companion app so more players will use it.

In general, the companion LFG is best for PS4, Xbox has their dashboard LFG (though the companion LFG still works well), and Steam users are probably using Discord, because the companion app can't auto-join you on steam. I hope to eventually find a solution that brings all of the platforms to parity, but that is a much longer term project.

After managing your inventory (which can be done directly in the app or by using the official API via DIM or other 3rd party apps), it is our most popular feature by far.

Make sure you haven't set your privacy options too tightly. Especially on PS4, you can set your system privacy settings so tightly so you can't send/receive invites except with your friends.

Most of the fireteam functionality is in the API. However, due to platform restrictions of Xbox and PSN (you need the auth token for them, which you don't have on the 3rd party apps), we can't expose the invite functionality in the API. So, you can build fireteams, but not send invites like the companion app does for consoles. Eventually, we hope to build something that doesn't need to route through the consoles' services that would work for Steam as well, but that is a long term project.

Thanks to our robust API support, there are lots of great alternatives to the companion app that replace all or some of its functionality. Such apps can very specifically focus on certain aspects to the exclusion of everything else, and innovate in those areas, and are often very good. DIM is a great one, so is Ishtar Commander. We've been looking into ways to better highlight these efforts in our companion and website so people can know about them. The official app will remain as the "entry point" generalist tool, but we want to spread to word about all the great work our community does with our API.