The file is generated specifically for your computer. It contains the authorization code that unlocks the software. Think of it like a unique password that only works on the specific machine for which it was generated. Without this file, Ableton Live 11 will remain in "Trial" or "Unauthorized" mode, restricting saving and exporting capabilities after the trial period ends.
An .auz file is a unique registration key generated by Ableton's servers specifically for your computer hardware. It is required to enable essential features like your work if your computer cannot connect directly to the internet. Step-by-Step Offline Authorization Ableton Live 11 Authorize.auz File Download