you can "determine" by the hairs on your neck, etc. I always believe that more data is better. True vs. apparent is an obvious benefit, but if the instrument is part of a network you can have the autopilot sail the boat via the apparent wind angle. As a cruiser, I don't want to be constantly "tweeking" the sheets, so the AP moves the boat in 5 - 10 degree movements to maintain the angle and in many situations keeps the speed up a little more. This requires a lot of open water and little other boat traffic, but it can be fun.