Sitemap gen apache log technique coupled with already existing sitemap : am i right ?

Sitemap gen official google software handle various techniques to
generate a sitemap.
the one based on apache log exploration, mixed to already sitemap gen
autogenerated sitemap seems to be the most managable for big dynamic
sites.

What i understood is that the script browses your apache log, then your
already existing sitemap, and then compare, and compile 1 or more new
sitemaps.
That have a snowball effect on your sitemaps files, that will keep
already apache logged urls, and add new ones each time it s ran, i m i
right ?

Here is what i have done with my sitemap config xml :

<?xml version="1.0" encoding="UTF-8"?>
<site base_url="http://www.mydomain.com/"
store_into="/var/www/html/mysubdir/sitemap.xml.gz" verbose="1" >
<accesslog path="/var/log/apache/access.log" />
<sitemap path="/var/www/html/mysubdir/sitemap.xml.gz" />
</site>
(etc + some filters )