Although there is value in performing all kinds of rep ranges, especially if you are looking to sculpt a strong, muscular and toned looking body…there are some people and disciplines that require you to be more specific. For example, it may be somewhat counter-intuitive for a powerlifter to regularly perform high rep ranges, clearly in order to perform high reps you need to have a relatively light weight on the bar… and this is not conducive to powerlifting. A powerlifter would be better served performing relatively low reps of say around 5-6, with a weight that sees them really struggle on the final rep of each set, this is strength training and is much better suited to powerlifting.
A bodybuilder’s sole goal is to increase muscle mass, definition and aesthetics. In order to achieve this some heavy weight has to be lifted along the way, but more often than not a bodybuilder will benefit from hypertrophy training i.e. a rep range of say 10-12 using an appropriate weight that sees them struggling on the final rep. This type of rep range will cause a sustained perfusion of blood to the muscle in order to stimulate growth.
Although a bodybuilder might also wish to tone their muscles, one of the main ways they do this is by increasing lean mass. Lean mass is metabolically active and burns a lot of calories when at rest, the result is fat loss. A regular person wanting to tone and define may prefer to opt for a high rep range of around 15- 20 reps, this means the person will have to tax their cardiorespiratory system in order to maintain the movement, the result is increased calorie expenditure and fat loss. These 15-20 reps may also be bodyweight movements such as press- ups, pull- ups or air squats which should see the individual breathing reasonably heavily after the exercise set.