These factors have contributed to email being a relatively informal medium. Several other email features make it quite handy. You don't have to search for most email addresses. Email programs organize addresses for you so that it takes only a moment to properly send a message to a correspondent. Also, your email messages can be kept in an electronic filing cabinet for later review.
Correspondence is much of what people traditionally put into filing drawers.
Doing this with the paperless medium makes it more efficient. Even with all the advantages, sometimes you have no choice but to use email. An example is when the only address you have for a person is their email address. To some people, the fact that email is free means that they choose to use it. Yes, for an individual.