When NOT to use yield (return) [duplicate]

Answer 1

I have to maintain a pile of code from a guy who was absolutely obsessed with yield return and IEnumerable. The problem is that a lot of third party APIs we use, as well as a lot of our own code, depend on Lists or Arrays. So I end up having to do:

IEnumerable myFoos = getSomeFoos();
List fooList = new List(myFoos);
thirdPartyApi.DoStuffWithArray(fooList.ToArray());

Not necessarily bad, but kind of annoying to deal with, and on a few occasions it's led to creating duplicate Lists in memory to avoid refactoring everything.