Here is a typical healer that can be used to a great effect in a team. Many players would doubt the need to have a healer as their ally, since every legend has an ability to revive their teammates. But Lifeline can do it 25% faster and under a protective shield, which guarantees the result.
She can also call upon an airdrop, which includes some additional protective gear. But that is basically it, and that is why Lifeline is so low on our tier list of Apex Legends characters.