This sand is used for filling holes made on the golf course when you take turf (a divot) with your shot and leave it stripped to the dirt.
In the fairway, replacing divots with sand is also important. If you're sitting and waiting for your turn to play and see a huge hole in the fairway, feel welcome to fill it. You're performing a community service for all the golfers when you do.
Sometimes sand also contains grass and fertilizer. This occurs most often in Spring and Fall when grass is able to get a better start. When sand is wet, sometimes it is easier to grab and handful than it is to take a scoop or pour.