Perhaps the most apparent is to increase 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 components and also lubricants. In general, be prepared to spend more for quieter, smoother gears.
Don’t make the mistake of over-specifying the engine. Remember, the insight pinion on the planetary should be able manage the motor’s output torque. What’s more, if you’re utilizing a multi-stage gearhead, the result stage must be strong enough to soak up the developed torque. Obviously, using a better motor than necessary will require a bigger and more expensive gearhead.
Consider current limiting to safely impose limitations on gearbox size. With servomotors, output torque is usually a linear function of current. Therefore besides safeguarding the gearbox, current limiting also protects the electric 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 concurrently in mesh. Although you can’t really totally eliminate noise from this assembly, there are many ways to reduce it.
As an ancillary benefit, the geometry of planetaries matches the shape of electric motors. Therefore the gearhead can be close in diameter to the servomotor, with the output shaft in-line.
Highly rigid (servo grade) gearheads are usually more expensive than lighter duty types. However, for rapid acceleration and deceleration, a servo-grade gearhead could be the only sensible low backlash gearbox choice. In such applications, the gearhead may be viewed as a mechanical spring. The torsional deflection resulting from the spring action increases backlash, compounding the effects of free shaft motion.
Servo-grade gearheads incorporate a number of construction features to minimize 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 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 component bearings. Small planetaries can often manage with low-price sleeve bearings or additional economical types with fairly low axial and radial load ability. For bigger and servo-grade gearheads, heavy duty result shaft bearings are usually required.
Like most gears, planetaries make noise. And 
the quicker they run, the louder they obtain.
Low-backlash planetary gears are also obtainable in lower ratios. Although some types of gears are generally limited by about 50:1 and up, planetary gearheads extend from 3:1 (single stage) to 175:1 or more, depending on the amount of stages.