You should register a Domain Name for a number of reasons:
They are scarce.
Internet Domain Names are a rapidly diminishing commodity. They are allotted on a first-come first-serve basis.
They are important.
The Internet Domain Name has become a vital part of corporate identity.
In the 21st Century, your Domain Name will be as important as your trademark and your presence in a global marketplace.
They are versatile.
For example, any email addressed to you at email@example.com can be forwarded to your current email address.