Article Announcement Sites - What´s the benefit?

hi

I´ve been submitting articles to article and PR sites for a while now but I´ve been told I should also be submitting to Article Announcment sites.

Here I´m having a little trouble working out what the benefit would be - any clues?

I´ve joined some Yahoo groups but again am at a loss to understand how these will be of that much benefit - I´m looking to use it less as marketing and more as a link building exercise.