Similar to pmx's point, an implicit assumption in this (which is unlikely to be true in many scenario's) is that the there is a negligible spread in the distrib

Similar to pmx's point, an implicit assumption in this (which is unlikely to be true in many scenario's) is that the there is a negligible spread in the distribution of revenue per customer. Imagine if you have one whale customer and a bunch of small fish, if you lose the whale in the change you won't maintain the same revenue. Some scenario's this assumption is reasonable though (say Netflix subscribers).