Imagine a clock that will keep perfect time forever, even after the heat-death of the universe.
A device known as a "space-time crystal," a four-dimensional crystal that has periodic structure in time as well as space. A space-time crystal could also be used to study phenomena in the quantum world, such as entanglement, in which an action on one particle impacts another particle even if the two particles are separated by vast distances.
The proposed space-time crystal is not a perpetual motion machine because being at the lowest quantum energy state, there is no energy output. However, there are a great many scientific studies for which a space-time crystal would be invaluable. Source
But who's going to give a damn what time it is after the heat-death of the Universe
At the heart of science is an essential balance between two seemingly contradictory attitudes--an openness to new ideas, no matter how bizarre or counterintuitive they may be, and the most ruthless skeptical scrutiny of all ideas, old and new.
This is how deep truths are winnowed from deep nonsense. -- Carl Sagan
The OP article points out some of the "practical" values of this new possibility. Only time will tell what benefits Mankind may gain. It's a potential tool for studying and understanding our universe. One example from the article:
With such a 4D crystal, scientists would have a new and more effective means by which to study how complex physical properties and behaviors emerge from the collective interactions of large numbers of individual particles, the so-called many-body problem of physics.