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 can be suffering from gear 
and housing components as well as lubricants. In general, be prepared to spend more for quieter, smoother gears.
Don’t make the error of over-specifying the electric motor. Remember, the insight pinion on the planetary must be able deal with the motor’s output torque. What’s more, if you’re utilizing a multi-stage gearhead, the result stage must be strong enough to absorb the developed torque. Obviously, using a more powerful motor than necessary will require a larger and more costly gearhead.
Consider current limiting to safely impose limitations on gearbox size. With servomotors, output torque can be a linear function of current. Therefore besides safeguarding the gearbox, current limiting also protects the motor and drive by clipping peak torque, which can be anywhere from 2.5 to 3.5 times continuous torque.
In each planetary stage, five gears are at the same time in mesh. Although it’s impossible to totally get rid of noise from such an assembly, there are several methods to reduce it.
As an ancillary benefit, the geometry of planetaries matches the shape of electric motors. Hence the gearhead can 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 acceleration and deceleration, a servo-grade gearhead could be the only wise choice. In this kind of applications, the gearhead could be seen as a mechanical spring. The torsional deflection caused by the spring action adds to backlash, compounding the effects of free shaft movement.
Servo-grade gearheads incorporate a number of construction features to reduce torsional stress and deflection. Among the more prevalent are large diameter output shafts and beefed up support for satellite-gear shafts. Stiff or “rigid” gearheads tend to be the costliest of planetaries.
The kind of bearings supporting the output shaft depends on the load. High radial or axial loads generally necessitate rolling element bearings. Small planetaries can often manage with low-cost sleeve bearings or other economical types with fairly low axial and radial load capacity. For bigger and servo-grade gearheads, heavy duty result shaft bearings are often required.
Like the majority of gears, planetaries make noise. And the quicker they operate, the louder they obtain.
More information about low backlash gearbox could be found below.