In some small projects I have built with elm, I use to wrap my development using Dockerfiles manually and combining them using docker-compose.
Using toast this can all be reduced into 1 neat yaml file.
The main benefit with this technique is that anyone can come into the project, install toast, run the command and start coding right away.
The main benefit that I see is the convenience provided here.
Instead of having to docker docker build . -t some_name && docker run -p PORT:PORT -v VOLUME:VOLUME some_name or maintaining two files and doing docker-compose up for self standing apps, its simply toast.
On the other hand, if the production version is using docker-compose it might be beneficial to just use that locally as well.