1) a site or email service couldn't change hosting providers (and hence IP) without breaking all links and bookmarks
2) you couldn't have more than one site or email namespace hosted on the same machine, since the server wouldn't be able to distinguish them
Having a layer of indirection gives you much more flexibility.
And if you don't really care about the name, you can a domain for less than $2/y on one of the new TLDs.
1) a site or email service couldn't change hosting providers (and hence IP) without breaking all links and bookmarks
2) you couldn't have more than one site or email namespace hosted on the same machine, since the server wouldn't be able to distinguish them
Having a layer of indirection gives you much more flexibility.
And if you don't really care about the name, you can a domain for less than $2/y on one of the new TLDs.