In general, no. However, we would strongly recommend that you
install, at a minimum, the ``base'' source kit, which
includes several of the files mentioned here, and the
``sys'' (kernel) source kit, which includes sources for the
kernel. There is nothing in the system which requires the
presence of the sources to operate, however, except for the
kernel-configuration program
config. With the exception
of the kernel sources, our build structure is set up so that you
can read-only mount the sources from elsewhere via NFS and still
be able to make new binaries. (Because of the kernel-source
restriction, we recommend that you not mount this on
/usr/src directly, but rather in some other location
with appropriate symbolic links to duplicate the top-level
structure of the source tree.)
Having the sources on-line and knowing how to build a system with them will make it much easier for you to upgrade to future releases of FreeBSD.
To actually select a subset of the sources, use the Custom
menu item when you are in the Distributions menu of the
system installation tool. The src/install.sh script
will also install partial pieces of the source distribution,
depending on the arguments you pass it.