Outliers are individuals that are very different from the majority of the population. Traditionally, among practitioners there is a certain mistrust in outliers, this is why ad-hoc measures such as removing them from the dataset are often adopted.
However, when working with real data, outliers are on the order of business. Sometimes, they are even more important than other observations! Take for instance the case of individuals that are outliers because they are very high-paying customers: you don’t want to discard them, actually, you probably want to treat them with extra care.