Is there ever a reason to not use 'yield return' when returning an IEnumerable?

Question

Simple example - you have a method or a property that returns an IEnumerable and the caller is iterating over that in a foreach() loop. Should you always be using

Answer 1

I don't think so. As @LBushkin suggests, if you were going to return something as a whole, you'd return an IList or whatever. If you're returning an IEnumerable, people expect deferred execution, so I think you should always use yield in that case.