Emphasizing a significant difference:
* The new software vastly improved the company's efficiency.
* The two candidates' views on healthcare vastly differed.
* The cost of living in the city vastly outweighed the benefits.
Describing something large in scope or extent:
* The Amazon rainforest is vastly larger than any other forest in the world.
* The museum's collection of ancient artifacts was vastly impressive.
* The universe is vastly more complex than we can currently comprehend.
Note: "Vastly" is often used to emphasize a significant difference or magnitude. It can also be used in a more literal sense to describe something large in size or scope.