Port install never uses packages, always compiles from source - why?

[Lothar Haeger]

So I was wondering why it seems "port install" is always end up building from source on my machine and came across this in archive_sites.conf:

> #   prefix: The prefix of the MacPorts installation used to create the
> #       source's archives. This must match the value of "prefix" set in
> #       macports.conf, or the source is not used. Defaults to
> #       "/opt/local".
> #
> #   applications_dir: The applications directory of the MacPorts
> #       installation used to create the source's archives. This must
> #       match the value of "applications_dir" set in macports.conf, or
> #       the source is not used. Defaults to "/Applications/MacPorts".
> #
> #   frameworks_dir: The frameworks directory of the MacPorts
> #       installation used to create the source's archives. This must
> #       match the value of "frameworks_dir" set in macports.conf, or the
> #       source is not used. Defaults to "[prefix]/Library/Frameworks".

Does that apply to the default source? 

I've changed "applications_dir" because I like my apps in /Applications - could that simple change result in effectively disabling port's ability to install from pre-built archives?

Cheers, Lothar