The auto-recovery feature of Illustrator autosaves a copy of your files at regular intervals. You can recover your files, which are not manually saved, from the following locations:
[Windows] C:\Users\<username>\AppData\Roaming\Adobe\Adobe Illustrator [version] Settings\en_US\x64\DataRecovery
[macOS] < your username>/Library/Preferences/Adobe Illustrator [version] Settings/en_US/Adobe Illustrator Prefs
The backup will help you recover unsaved document data when your Illustrator crashes or you accidentally delete your files or close Illustrator without saving the files.
For more details, see Protect your files from a crash.