Shellys are amazing. We use the pucks everywhere for anything that’s not innately smart.
Some of our use cases:
Kitchen cabinet lighting that syncs each strip with each other as well as the overhead lights. Or the cabinet lights can be turned on independently.
Garage door opener, because MyQ sucks (it’s hooked up to a real physical garage opener button and triggers the button for us)
Outlet power monitoring (mostly for fun)
Can be put in light switch boxes in lieu of something like Kasa switches, but the physical switch won’t follow the light state any more. Similarly, smart wall outlets for power toggling