"Oh the PhD pinned to a nightly version of some dep and the AUC score plummets when you try to upgrade and customer wants this latest model in production on airgapped machines last week? Aight, stick their Conda env in a container, call it with `docker run`, and sort it out later"
Horrifying? Yes. Solving the problem on short notice? Also yes.
Plenty of more pedestrian uses but that was an actual situation where docker's reproducibility saved my bacon.