It fixes more bugs, so you should install it, particularly if you've found some features on your iPhone are acting weird.
iOS 13.1.2 fixes an issue where the iPhone's camera might not work at all. It also addresses a "bug where the progress bar for iCloud Backup could continue to show after a successful backup," according to the change log. The release also patches bugs related to the flashlight not opening properly, display calibration issues, a problem related to running shortcuts on the HomePod and a bug where the iPhone's Bluetooth connection could be lost in some cars.
You can install iOS 13.1.2 by opening Settings > General > Software Update on your iPhone.