Why do we need to set up AAI PT by default in the system

Product: JDE E920.

Hi, I would like to know why do we need to set up AAI PT to a Tax account by default.

I know we need to set up the AAI PTxxx, where xxx is the GLOffset related to the taxarea, in order to automatically impact the taxaes to the account we set up.

But why do we need to set bu default the AAI PT? And what kind of account should be realted to?

Thanks!

Ezequiel