Perhaps the most apparent is to increase precision, which is a function of manufacturing and assembly tolerances, gear tooth surface finish, and the guts distance of the tooth mesh. Sound is also suffering from gear and housing materials along with lubricants. In general, expect to pay more for quieter, smoother gears.
Don’t make the mistake of over-specifying the motor. Remember, the insight pinion on the planetary must be able handle the motor’s result torque. What’s more, if you’re utilizing a multi-stage gearhead, the result stage should be strong enough to soak up the developed torque. Obviously, using a more powerful motor than required will require a bigger and more expensive gearhead.
Consider current limiting to safely impose limits on gearbox size. With servomotors, result torque is definitely a linear function of current. Therefore besides protecting the gearbox, current limiting also shields the electric motor and drive by clipping peak torque, which may be from 2.5 to 3.5 times continuous torque.
In each planetary stage, five gears are simultaneously in mesh. Although you can’t really totally get rid of noise from this assembly, there are many methods to reduce it.
As an ancillary benefit, the geometry of planetaries fits the shape of electric motors. Thus the gearhead could be close in diameter to the servomotor, with the result shaft in-line.
Highly rigid (servo grade) gearheads are generally more costly than lighter duty types. However, for speedy low backlash gearbox acceleration and deceleration, a servo-grade gearhead may be the only sensible choice. In this kind of applications, the gearhead could be viewed as a mechanical spring. The torsional deflection resulting from the spring action adds to backlash, compounding the effects of free shaft motion.
Servo-grade gearheads incorporate a number 
of construction features to reduce torsional stress and deflection. Among the more common are large diameter result shafts and beefed up support for satellite-gear shafts. Stiff or “rigid” gearheads have a tendency to be the costliest of planetaries.
The kind of bearings supporting the output shaft depends on the strain. High radial or axial loads usually necessitate rolling element bearings. Small planetaries can often get by with low-cost sleeve bearings or additional economical types with fairly low axial and radial load capability. For larger and servo-grade gearheads, heavy duty output shaft bearings are often required.
Like the majority of gears, planetaries make noise. And the faster they run, the louder they get.
Low-backlash planetary gears are also obtainable in lower ratios. While some types of gears are generally limited by about 50:1 or more, planetary gearheads prolong from 3:1 (solitary stage) to 175:1 or more, depending on the number of stages.