Every manufacturer provides maintenance/service intervals. Mileage, environment (clean/dirty), usage, temperature and more will be considered and outlined in terms of when & what is too serviced.
Oil that is not replaced according to manufacturer's intervals will deteriorate and the lubrication and cooling ability will decrease. This in return will increase wear and tear on the engine components ultimately resulting in increased oil consumption.
The oil deteriorates due to heat, contaminants, combustion by-products, friction and life expectancy of the additives. Once it deteriorates past a certain point it will start turning into sludge failing to provide lubrication and cooling properties.
In addition to ensuring that the oil change intervals are adhered to, it is also essential to that the key adjustment values and test values are checked and if necessary corrected during the maintenance work. These will be documented in the work shop manuals.