Typically string key maps should exist only at the edges of your system, but they are still often necessary when you're interacting with the outside world. Para

Typically string key maps should exist only at the edges of your system, but they are still often necessary when you're interacting with the outside world. Params in Phoenix come in as a string key map because the atom table does not get garbage collected, so where you don't know what keys may be passed in, string keys are necessary to avoid the risk of running OOM. That said, once I know the shape of the data I'm dealing with, I pretty much always convert to an atom key map as quickly as possible. If I see a string key outside of the context of a controller or worker, I am immediately suspicious.