Appare Vestigium is the incantation of a tracking spell that illuminates the area it is being used in a swirl of gold that reveals recent magical activity.
This could have been used many times in the Harry Potter series, namely when the Philosopher's Stone was stolen, to see who stole it, the culprit behind the petrification of Mrs. Norris, Colin Creevey, and Hermione, and in the Goblet of Fire, to see who put the name in the Goblet of Fire, and to see who cursed Katie Bell.
HERE are the BIGGEST ONES!
The years that Voldemort, then Tom Riddle, attended Hogwarts after those nasty incidents.
The houses of Death Eaters when they were arrested following the end of the First Wizarding War. This would have revealed lots of information as well as maybe leads, such as Lucius Malfoy, on the then-current whereabouts of Voldemort.
The return of Voldemort. Dumbledore and, to conclusively convince the entire Wizarding World, Ministry officials could have gone to Little Hangleton to check on what happened between Cedric, Harry, Peter Pettigrew, Voldemort and the 30 Death Eaters (2 and 1/2 Death Eaters in the Goblet of Fire novel = 2.5 * 12 = 30).
Why wasn't Appare Vestigium used by Dumbledore and the other high-ranking Ministry members?
Newt was a student of Dumbledore, who he remained very close to even after expulsion (Dumbledore vouched for him to stay in Hogwarts) and brother of Theseus, a well-respected Auror. Aurors are hired by the Ministry, so Theseus must have known this spell as well, or at least, likely to have known it.