Its importance in the future will, in all likelihood, continue to grow at an almost exponential rate. Email has the advantage of regular postal mail in that it is delivered into the recipient's mailbox for them to read and reply to at their convenience, but without the lengthy time delay involved with 'snail mail'.
Email also has the advantage of being quick and easy.
It doesn't oblige the sender to engage in small-talk with the recipient, as telephones do. In an increasingly busy world, email allows the same message to be conveyed in a minute or two without implied rudeness. Email is an electronic version of a written Memorandum. The term 'Cc' is retained because it still somehow makes sense to people even though the days of making an actual 'carbon copy' are long gone. Many people under the age of 40 will have never seen a sheet of carbon paper, such as was used in offices to make a copy in a typewriter of the original memo.