Applications
Gear couplings use backlash to allow for angular misalignment.
Backlash is undesirable in precision positioning applications such as machine tool tables. It can be minimized by tighter design features such as ball screws instead of leadscrews, and by using preloaded bearings. A preloaded bearing uses a spring or other compressive force to maintain bearing surfaces in contact despite reversal of direction.
There can be significant backlash in unsynchronized transmissions because of the intentional gap between dog gears (also known as dog clutches). The gap is necessary so that the driver or electronics can engage the gears easily while synchronizing the engine speed with the driveshaft speed. If there was a small clearance, it would be nearly impossible to engage the gears because the teeth would interfere with each other in most configurations. In synchronized transmissions, synchromesh solves this problem.
Read more about this topic: Backlash (engineering)