Perhaps the most apparent is to improve precision, which is a function of manufacturing and assembly tolerances, gear tooth surface finish, and the center distance of the tooth mesh. Sound is also affected by gear and housing materials and also lubricants. In general, be prepared to pay out more for quieter, smoother gears.
Don’t make the error of over-specifying the engine. Remember, the input pinion on the planetary must be able handle the motor’s result torque. Also, if you’re utilizing a multi-stage gearhead, the output stage should be strong enough to soak up the developed torque. Certainly, 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 usually a linear function of current. So besides safeguarding the gearbox, current limiting also shields the electric motor and drive by clipping peak torque, which can be from 2.5 to 3.5 times continuous torque.

In each planetary stage, five gears are concurrently in mesh. Although you can’t really totally remove noise from such an assembly, there are several ways to reduce it.

As an ancillary benefit, the geometry of planetaries fits the shape of electric motors. Hence 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 acceleration and deceleration, a servo-grade gearhead may be the only wise choice. In such applications, the gearhead may be viewed as a mechanical spring. The torsional deflection resulting from the spring action adds to backlash, compounding the effects of free shaft movement.
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 tend to be the most costly of planetaries.
The kind of bearings supporting the output shaft depends on the strain. High radial or axial loads generally necessitate rolling component bearings. Small planetaries can often manage with low-price sleeve bearings or other economical types with fairly low axial and radial load capacity. For larger and servo-grade gearheads, heavy duty output shaft bearings are often required.
Like most gears, planetaries make sound. And the faster they run, the louder they get.

This is just how low backlash gearbox can be used for your advantage.