MIA for the weekend, so late in my reply.

We have a true/apparent wind instrument and still look at the Windex out of habit. But often by the end of the season a bird has sat on it and so it's useless. Of course you should be able to sail perfectly well without any instruments and I can tell time pretty well without a watch. But it's nice to have all these as unbiased observers.

Just like a water speed indicator is interesting to compare to GPS over ground, so is true to apparent wind. I use apparent when going upwind just like the Windex. Downwind I find true wind provides a better gauge of gybe angle, or how not to gybe angle as it were. (On an AC 32, probably need apparent all the time!)

As someone mentioned, you can be lulled downwind into not realizing how hard it's blowing and not be prepared when you turn into the wind. Sure, you should know, but more is better. And it may be useful information for others on board, even if you know.