You can gain solid data on what the wind is doing to your heading while under sail. On each leg, you can watch your heading change in headers and lifts and you can begin to really visualize the patterns in the wind from either geographical features or oscillating patterns. Once you learn to use a compass, it will give you another tool to "see" the wind.

You can also use it to determine how square the start line is and if one end is favored or not.