[d-i manual] translation issue

[philippe.batailler@free.fr (Philippe Batailler)]

Hi all,

The d-i manual,
installer/doc/manual/en/appendix/chroot-install.xml,
reads:

<command>debootstrap</command> can use the
<filename>basedebs.tar</filename> file, if you have already downloaded
it ahead of time. The <filename>basedebs.tar</filename> file is
generated only every once in a while, so you'll get the latest version
of the base system by pointing <command>debootstrap</command> directly
to a Debian archive as shown in the previous section.

What does " only every once in a while " mean?

Is it:
The basedebs.tar file is generated if you need it and only if you need it,
so you'll get the latest... ?

or something else ? 

Thank you very much for any answer.
Regards,

-- 
Philippe Batailler