If I'm using them together, I'll start off a pipeline with a big DT expression, then pipe it through a few dplyr verbs as a kind of "post processing."

I find that some tasks are frustrating with one package but easy with the other, so more frequently I just have some "dplyr lines" and some "data.table lines" in my scripts.

And the compatibility between the two has improved a lot, so you don't get so many "invalid selref" warnings and unexpected behavior when you combine them in pipelines