But everyone will vary on that. Some sail their boats just like dinghys(mine is not much more complicated), the wind direction and speed is what you glean from experience of what you see and feel. That's true wind, apparent, and if it's growing downwind(I always assume it is!)
But from a safety standpoint, I have to see the waves and wind, the edges of sails and how they are reacting to the gyrations of the boat in the waves.
I live in fear of crash jibes so I want to be able to place the sail angles at what is safe for the conditions, especially at night. The idea that the only thing between me and a crash jibe at night is 4" dial in my lap, is terrifying!