We use the term "theme" rather than "epic" but it's in the same ballpark in terms of "thing used to gather issues together". However, we don't use them to represent features, instead we use them to represent initiatives or goals. We try to work in a way that we're focused on the outcome (what does doing this work accomplish for our users) rather than the output (which features are we going to ship). This in turn means that a theme is not done when the code is completed. Instead we need to follow up on metrics, feedback, etc. and ensure that we got the outcome we were after.

Disclosure: I'm the founder of kitemaker.co, an issue tracker that is quite focused on themes and trying to help teams improve.