As iMore points out, in the Touch ID section of the Settings app on macOS 10.14.4, there's a new "Safari AutoFill" listing you can enable.
With Safari AutoFill enabled for Touch ID, you can place a finger on the Touch ID home button to automatically fill in web form content.
Right now, you can use AutoFill to enter usernames, passwords, addresses, phone numbers, and credit cards, and more right into web pages, but you generally have to click into a form and then start typing before the AutoFill option comes up.
It sounds like the new Touch ID Safari AutoFill feature will streamline the process, filling forms with a touch.
macOS 10.14.4 also expands Apple News to Canada and it introduces automatic dark mode themes for websites, so if you have Dark Mode enabled and visit a website that has a dark theme available, it will be activated automatically.