When doing lateral arm raises most athletes raise their arms to the shoulder level position, i.e., so that the arms are level with the floor. This is the highest they can go when using heavy weights — usually over 20 pounds!. However such execution limits the range of motion and creates excessive forces in the shoulder joint. This in turn can lead to shoulder problems.
To counteract the negative consequences you should also do lateral arm raises through the full range of motion. This means bringing straight arms completely overhead so that you can clap hands. By doing this you elicit an even greater contraction of the deltoid, especially the middle deltoid, and some of the other muscles involved. At at the same time you lessen the chance of injury.
In order to raise the arms to the full overhead position you will not be able to use heavy weights. Usually 5 to 15 pounds is more than adequate. Such light weights trick most athletes into believing that this exercise is inferior, but in reality it is not. Not only do you get excellent muscle development but you also maintain a free shoulder with a full range of motion. This is especially important for all throwing athletes.
The act of raising the arms only to the level, or slightly below level position when using heavy weights, often causes tightening in the shoulder joint. This results in limited flexibility which in turn can lead to shoulder impingement. Shoulder impingement and related problems are common injuries among athletes.
Aesthetically, lateral arm raises to the completely overhead position does more than any other exercise (except possibly the overhead press) to shape the outside contour of the shoulders. It gives width to the shoulders and a V-shaped appearance to the body (as opposed to a pear shape when the shoulders are narrow and the pelvic girdle is wide).
Shoulder joint abduction (raising the arms sideways) is a very important action in all sports that require you to raise your arms. This includes blocking in basketball and volleyball, reaching the apparatus in gymnastics, catching overhead flies in baseball, the guarding stance and rebounding in basketball and in swimming during stroke recovery. However, these movements are not done against a heavy resistance.
For more information, see Biomechanics and Kinesiology of Exercise.