Everything that has some kind of engine will eventually be worn out
What does it mean to service a watch?
Mechanical movements consist of a bunch of small components. Many of these components have constant stress and friction on them. To make the components work properly, some parts are also lubricated with various oils.
When something has constant stress and friction, it will eventually get worn out, and maybe even break. Lubricants can also run dry, and make it harder for the moving parts to move. These are things that can affect how your movement acts, and when it may be in the need of a service.
While many of the parts in a watch movement can last for many years, decades even, some parts are more vulnerable and will get worn out faster than other.
How often should you service your watch?
Different brands have different warranties, but different brands also make their movements in different ways and with different philosophies, so this is something that will also affect how often you need to service your watch.
Watch companies will often suggest you get a service every 4-5 years,
What happens if you don’t service a Watch?
After 5 years the oils and gaskets need replacing along with the crown and tube and will need internal cleaning. Without servicing your watch won’t last as long as it has been engineered and designed to.