Can be useful when you have multiple monitors and don't want to clutter the main window, especially for single page apps or visualization/monitoring things.

I have done my own take at this since some times but vanilla only https://github.com/grz0zrg/wui where any of the dialog widget can be detached off the main window keeping the same content & state. A feature i never saw in any web apps but saw often on desktop apps, nice to see that some peoples think of this sort of thing with cleaner approach!