Can not figure out what custombuild is

I have read many topics, but I can not figure it out what it is and what is does!
Can someone tell me what custombuild now exactly is, and why it is good to install or not? What are the benefits?

I need to install directadmin in a few days, so i’m wondering if I need custombuild?
And how can i install custombuild with the directadmin installation?
I have read that there is a configuration file: options.conf Do i need to set the options before install, or is it asked while installing?

Any explanation will be great