Why do my Coroutines allocate memory when they execute?

I’m optimizing GC on a project compiled with Unity 5.3 Win 8 64bit which uses Coroutines like this:

public override void Start() {
IEnumerator MyCoroutine() {
	while (true) {
		yield return 0;

According to the profiler, the example above allocates 37B (shallow profiling) 20B (deep profiling) of memory on every frame:

I couldn’t find much info about this - is it a known issue? Does it happen in production and/or mobile builds? Is it worth avoiding Coroutines when ram or GC spikes are a concern?

And could this be related to the bug in Mono which causes unnecessary boxing when iterating through a List using foreach (as opposed to for int i;;)? I wonder if both are calling MoveNext() at some level.

Don’t yield “0”. An IEnumerator is based on the type “object”. If you want to wait one frame return null. The value 0 is an integer which need to be boxed on the heap so it can be returned as object.