Very handy for nav bars with expandable drop-downs for more links - can now be done with zero JS. Requires much less CSS boilerplate now, and you don’t have to use z-index at all (which eliminates a whole bunch of tricky issues). They also handle all the tricky aria/keyboard/focus mgmt bits for you, too. It works really, really well.
Supposed to be real handy for tooltips too, but haven’t used that myself yet.
Edit to avoid potential confusion: these are separate from modal dialogs, think more like very small popups anchored to one point on the page that still allow you to interact with everything else. Theoretically you can make them modal, but it would be silly to - you’d be better off using <dialog> and the invoker api
Supposed to be real handy for tooltips too, but haven’t used that myself yet.
Edit to avoid potential confusion: these are separate from modal dialogs, think more like very small popups anchored to one point on the page that still allow you to interact with everything else. Theoretically you can make them modal, but it would be silly to - you’d be better off using <dialog> and the invoker api