There are generally two types of soil. The first is dry soil, including substances like grit and sand, which fall to the bottom of the carpet. This type of substance is abrasive, so if it’s not removed it will start to damage fibres over time. Regular vacuuming will remove all dry soil.
The second type of soil is best described as ‘sticky’, which includes any dirt brought into the house on shoes and air pollution. This type of soil can attract more dirt (known as re-soiling) if not periodically removed.
So it’s also a good idea to have your carpet cleaned professionally – annually or every couple of years depending on level of usage – to remove general sticky soil which accumulates on any floor surface over time.