[Serusers] why combine ser with asterisk

Hi All, What's the advantage of combining ser with asterisk? I always see comments like using ser with asterisk is a very good solution etc. etc. the thing i liked with ser is that it does not do codec translation, which saves me cpu usage and also bandwidth. if i combine it with asterisk, would it not use codec translation? i also read that there is also a problem when ser and asterisk is run on the same machine, why is it so? if use prepaid billing solution for asterisk like astcc, would i then be able to provide prepaid service? soryy for asking too much, i'd just like to really understand it. Thank You in advanced. Regards, Nhadie