I'd say the real advantage is that if you need to change it you don't have to deploy your monolith. Of course, the relative benefit of that is situationally dependent, but I was recently burned by a team that built a new replication handler we needed into their monolith, and every time it had a bug, and the monolith only got deployed once a week. I begged them to put it into a lambda but every week was "we'll get it right next week", for months. So it does happen.