Like any high-precision instrument, a watch needs to be serviced regularly in order to work perfectly. Obviously, we cannot indicate the intervals for such work, which depends on the model, climate and the care taken by the watch's owner.
The small amount of oil needed to lubricate the bearings of the movement gets used up. This can lead to reduced accuracy or even stop a movement. Also the crown can get damaged by hits and the little rubber seals that guarantee the tightness of the watch dry up over time, letting dust and humidity enter the movement.
As a general rule, service intervals are between 3 and 7 years, depending on the use.
