Most companies will tell you that 80% of their business comes from 20% of their customers.
This is the 80-20 rule, also known as Pareto’s Law, named after Italian economist Vilfredo Pareto, who observed in 1906 that 80% of the land in Italy was owned by 20% of the population, and that 20% of the pea pods in his garden contained 80% of the peas (Wikipedia).
That being the case, how companies communicate to their existing customers is crucial to their financial success. (How they communicate to people who are not yet customers is an entirely different subject that we will cover later.) Most companies publish newsletters or magazines for distribution to their existing customers, showcasing their product changes, upgrades, staff re-shuffles and the like.