There is never a tail wind. It's just a good day.

A head wind is just the way it is, a metaphor for my life, or a theme for Bob Seger...

I think I read the same article C.M. did, complete with diagrams.
A 3/4 tail wind is the cat's pajamas.

In my opinion, the headwind/tailwind thing is not a wash, but it's darn close.
Never seems like it while you're riding, though, but Mr. Garmin seems to confirm.
I just don't think the tailwind makes up for the cursing and frustration, if you allow yourself that.

While C.M. likes calm humid air, I've done triathlons in the dead air around NC coastal plain lakes.
While it's not wind, it sucks, and the entire field was much slower than I know them to be.
It seems thick.

I do like near-zero wind, though. No headwind, and a chance at consistency.
My best 40K triathlon leg was on a near-zero wind day. It was one less thing to worry about.

By the way, "calm" wind is less than 5 knots. Hardly calm if you're on a bike, though.
Also, a "standard" 5'x3' flag, straight out from the flagpole, takes about 12 knots.

I'm not a physicist, and my "sail area" is substantial, but I do watch the Big Bang Theory once in a while.