I agree. Someone said you don't need it if you make the bolts tight, but IMO that's exactly why you need it, to get the bolts tight because otherwise the wheel will move while you're turning the bolts as hard as you can.

I just wanted to confirm that this setup is really the most robust for getting the chain tension precise and securing it in that precise position. So far no one has said otherwise except that forward facing horizontal dropouts might be okay with a specially designed chain tug if the dropouts are long enough and horizontal enough to get the right adjustment, but I don't see too many like that.