I will do the math for everyone, since many of you are confused. If you are shooting 300 fps flat on the ground at 30 yards(90 ft), straight out, it takes the arrow .3 seconds to get to the target. The arrow is going 300 fps for 90 feet horizontally, so the math is easy. The arrow is initially not dropping, but it would be falling at 9.6 fps downward due to gravity when it hit the target. If you calculate it out, the arrow would drop 1.44 feet over that .3 seconds due to gravity. If you are in a tree stand at 15 feet, and the deer is 30 yards(90 ft) from you via a straight line, you have formed a right triangle. Therefore the distance from the bottom of the tree to the deer is 87.5 feet. You would therefore be shooting down at an angle of ~9.5 degrees below horizontal, so your horizontal velocity is now only 296 fps, not 300. Since you are aiming downward some, the arrow also now has a downward vertical velocity of 50 fps. If you divide 87.5 horizontal feet from the tree by the 296 fps horizontal velocity you now have from the stand, you get the same .3 seconds you get shooting 30 yards on flat ground with a horizontal velocity of 300 fps. This is because 30 yards in a straight line is 30 yards regardless of direction. Since the arrow was started downward at 50 fps, gravity will add another 9.6 fps of velocity to it, just like it did when you were shooting on flat ground. The average velocity would therefore be 54.8 fps downward, over the .3 seconds it takes to reach the target. 54.8 fps X .3 seconds = 16.4 feet. You are in the tree at 15 feet, which means you would have to account for a 1.4 foot drop due to gravity. This is the same 1.4 feet of drop that you get when shooting on flat ground. If you use a 20 yard pin to shoot 30 yards, you run the potential to shot low, because you are then only accounting for .64 foot of drop.

People get confused because they don't realize that gravity pulls downward at the same rate, regardless of how fas something is moving horizontally. Say four guys are standing together. One shoots a 30-06, one shoots a BB gun, one shoots a bow, and one rolls a golf ball off a table, and they all do it simultaneously. As long as they were all shot horizontally, from the same height, and on flat ground, both bullets, the arrow, and the golf ball would all hit the ground at the same time. The acceleration downward due to gravity is consistent for all of them. It has nothing to do with how fast they are going horizontally. How far they would drop is a function of time only. The arrow from a fast bow will "drop" less than one from a slower bow, only because it is in the air for a shorter period of time.