There is a terrible misconception that repetition ranges somehow have a special affect on your body. Some believe that you need 8-12 reps for hypertrophy (muscle growth) and 5-6 reps are just for building strength while anything over 15 reps only builds endurance. Well, I think that is totally ridiculous. If you can perform 50 reps with 200 pounds in the leg press and after some time you now can do 50 reps with 210 pounds then you have gotten stronger, built more endurance and could possibly have increased your muscular size - period.
Varying repetition ranges (that is if you want to mix it up and your body can handle the varying loads placed on it) can keep the body "off guard" and help prevent becoming stale, bored or plateaued. By using a varied range, you may find certain repetition ranges to be more suitable for different body parts or a particular movement and you can then set new goals for personal records.
Personally, I feel a higher than normal repetition range is safer for most individuals - beginners or the most advanced because it allows for lighter loads to be used so there are less compressive forces. But don't think lighter means easier - no, far from it. If these sets are worked hard (which they should be) then these high rep sets can be very challenging, enabling the trainee to build good strength and stamina with less joint stress. - Fred Fornicola