It provides a complete, familiar, desktop environment that can be used for basic desktop computing. I've been using Ubuntu MATE on the Pi to introduce my daughter to computing for several years now.
But, it is probably of more interest to makers and device hackers who want to target Ubuntu for their projects. You can prototype homebrew ARMv7 or ARMv8 based IoT devices in a comfortable desktop environment, including building and testing your apps as snaps (https://snapcraft.io). The full Ubuntu archive is available to you.
For hobbyist projects, you can stick with Ubuntu MATE for "deployment", even with the option to disable the X11 display server if it not an application requirement. But, if you have something more professional in mind then the applications and snaps you've prototyped with Ubuntu MATE can be used with Ubuntu server or Ubuntu Core (https://www.ubuntu.com/core) on one of the ARM-based reference platforms.
