One of the greatest features is that you can now run desktop apps as containers. Let me explain this better.
If we want to have a desktop-like an experience, probably for testing or whatever, you need to use VirtualBox which is again a big headache. This new feature called windows sandbox allows you to run untrusted apps on a desktop like environment which is containerized. So a containerized desktop will be running over another desktop and changes made on the containerized desktop will not be reflected on your actual desktop providing security. Transfering, copying files among the two desktops will be as easy as dragging and dropping or copy pasting.
This is a very cool and useful feature for developing and testing teams. Go ahead make use of it :)