Why? What do I stand to gain from using this? Marginal speed improvement in some cases and a lot of headache trying to debug it in other cases?

docker-compose offers an alternative. It doesn't offer any genuinely new functionality. It may work for you if you don't know how to use the other alternative, or the other alternative is inconvenient for you for some other reason, but if it's not, it's just an extra tool that you don't need.