Can it be advantageous for a method to return IOrderedEnumerable<T> instead of IEnumerable<T>?

Question

Can it be advantageous for a method to return IOrderedEnumerable instead of IEnumerable?

Answer 1

Only if you expect people to order that enumerable every time and would find it hard to figure out how to do this OR if you can provide a collection that implements that interface that can efficiently order its contents and is paired with an extension method that is aware of your collection.

Best option is to return a specific collection type (see Richter for details on that). 99 times out of 100 whoever gets even a simple enumerable can use the standard linq extension methods to order it if they want.