[gentoo-user] Kernel upgrading and linux symlink

[Harry Putnam <reader@newsguy.com>]

Looking at the kernel upgrade pages at 
  http://www.gentoo.org/doc/en/kernel-upgrade.xml

Its a bit confusing about the symlink creation.  I've wondered about
it a few times. 

At the top, you're told how to get the sources and then a discussion
of the symlink follows.

It appears you are expected to change the symlink to the newly
installed sources.

But then it says:
4.  Updating the /usr/src/linux symbolic link

  "Gentoo requires that the /usr/src/linux symbolic link points to the
  sources of the kernel you are running."

So if gentoo `requires' the symlink to point to the running kernel
why are we changing it to the newly installed but not yet compiled or
started kernel?

And in fact does it really matter if its pointing at the newly
installed or actual running kernel, when kernel compiling operations
take place?