If you assist with andromeda your heals spread to other teams and can keep them in the fight. I'm not sure why, but other heals like angel feather from Nike don't consistently heal other parties. If you're not using andromeda, you'll often notice people being forced out of the raid by damage and being unable to help you, while Andromeda usage tends to snowball the raid into your favor as other teams can heal your team back as they continue to swing and build turns. Many times I've noticed people assisting with Solomon and Arthur and other heroic souls and then peter out as they take too much damage and the original raid starter can't help them due to lack of healing keeping them in the fight too.