Perhaps the most apparent is to improve precision, which really is a function of manufacturing and assembly tolerances, gear tooth surface finish, and the center distance of the tooth mesh. Sound can be suffering from gear and housing materials along with lubricants. In general, be prepared to spend more for quieter, smoother gears.
Don’t make the mistake of over-specifying the motor. Remember, the input pinion on the planetary should be able deal with the low backlash planetary gearbox motor’s output torque. Also, if you’re using a multi-stage gearhead, the result stage must be strong enough to absorb the developed torque. Certainly, using a more powerful motor than necessary will require a larger and more expensive gearhead.
Consider current limiting to safely impose limitations on gearbox size. With servomotors, output torque can be a linear function of current. Therefore besides protecting the gearbox, current limiting also defends the 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 concurrently in mesh. Although it’s impossible to totally get rid of noise from this assembly, there are several methods to reduce it.
As an ancillary benefit, the geometry of planetaries fits the shape of electric motors. Therefore the gearhead can be close in diameter to the servomotor, with the result shaft in-line.
Highly rigid (servo grade) gearheads are usually more costly than lighter duty types. However, for fast acceleration and deceleration, a 
servo-grade gearhead may be the only sensible choice. In such applications, the gearhead may be viewed as a mechanical springtime. The torsional deflection caused by the spring action adds to backlash, compounding the consequences of free shaft motion.
Servo-grade gearheads incorporate many construction features to minimize torsional stress and deflection. Among the more common are large diameter output shafts and beefed up support for satellite-gear shafts. Stiff or “rigid” gearheads have a tendency to be the most costly of planetaries.
The kind of bearings supporting the output shaft depends upon the load. High radial or axial loads usually necessitate rolling component bearings. Small planetaries can often get by with low-price sleeve bearings or additional economical types with relatively low axial and radial load ability. For bigger and servo-grade gearheads, durable output shaft bearings are often required.
Like the majority of gears, planetaries make noise. And the quicker they run, the louder they obtain.
Low-backlash planetary gears are also available in lower ratios. While some types of gears are usually limited by about 50:1 and up, planetary gearheads expand from 3:1 (single stage) to 175:1 or even more, depending on the number of stages.