He has finally settled down.
He is finally settled down.
Does second one mean that the guy has married and started a good life? What about the first one? Which one would you prefer most?
Of course it depends on a bit more context, but He has finally settled down usually means found a stable place in life, like getting married as you mentioned.
However, it can also mean he was very upset, like after witnessing a tragedy or losing a loved one, and has finally calmed down.