Normally, companion apps are almost a complete waste of time. There's functionality, but nothing pressing enough to make them crucial. Even when they enhance the experience, the games are usually competent enough in their menu management that the app mostly just serves as an alternate means to accomplish something. Or, they'll come with some small dividend, a bonus for thinking about the game when you're away from the game.
Mass Effect: Andromeda's companion app is more than that. Well, sort of. It's still just a different way to click through menus, but Mass Effect: Andromeda's menus are bloated enough that this feels like a significantly more efficient way to do it.
Named Apex HQ (available on iOS and Android), it's mostly multiplayer-oriented and excels at giving an overview of your characters, their loadouts, and your overall progress (along with the ability to upgrade and tinker with everything). This is something that Mass Effect: Andromeda (full review here!) doesn't do particularly well. Simply put: It's less confusing on the app than in the game.
However, the bigger allure comes in managing your Strike Teams, the passive multiplayer squads you can send to tackle missions when you don't feel like doing them. In Andromeda's singleplayer, you have to be either on the Tempest or the Nexus to send Strike Teams into battle. This is a problem because a lot of time is spent far away from those locations. The app makes it so you can always check in on them, constantly reaping the benefits of their hard work.
There's a lot to keep track of in Mass Effect: Andromeda. It's overwhelming at times. This app won't help cut down on the bulk of everything but it will streamline it to some extent. That's enough to justify a download.