External Auth Script or local Auth

Greetings, I am using Freeradius ver 2.1.10 I have noticed that some commercial radius servers (with freeradius backend) using External script (php/perl or C code) to authenticate users. I just wanted to know that what are the additional benefits of using external auth script over freeradius own authentication (via rad-groups) ? I made my own bash script that runs fine for authentication by checking user status in my_users table like expiry, disable/enable, quota, uptime etc , but for heavy load network like 20-30k users, what is recommended? script or local groups? Regards, JZ <http:///>