What is yield return

Can understand yield return as lazy versus normal return as eager. In an iterator block, normal return returns the entire resultset at once. While yield return returns instance of IEnumerable (implemented by Array/List), and then returns one by one when we access the value (the index position will be noted for the next access). Iterators can be used to lazily generate a sequence of objects. So the code in the method only executed once we need the value (and it’s one by one)

Benefits: save memory by no need to iterate all the collection, ex: with .First() with predicate only execute 1 time, there is no need to loop all the collection.