sa_mail_body_size_limit and SA scanning

[Alex]

Hi,

I have a fedora22 system with amavisd-2.10.1 and spamassassin-3.4.1.
I've set my $sa_mail_body_size_limit to 200*1024, or what I assume is
200k. I understand that messages beyond 200k are still partially
scanned, so I'm a bit confused.

What is the point of the setting if messages are scanned anyway? The
documentation appears unclear.

Thanks,
Alex