Greetings from Loreto, Baja Sur, Mexico...

The calculated true wind speed can be a good reminder that it could be time to reduce sail while sailing downwind, also to cool the desire to sail while under the iron genoa when apparent wind seems adequate for sailing. It is just another tool. We noticed recently that our Raymarine unit bases its true wind calculation on water speed, not GPS speed, so bad water speed readings yield faulty true wind readings. When you are in strong tidal current situations, you'll also get skewed results. All that said, we find ours is useful.

And, as others have said, it is nice to get the wind direction by looking forward rather than up. (Note-- different velocity and direction at masthead can mislead regarding apparent wind/speed near deck)