We know that the best source for proving the occurrence of an event is contemporaneous documentation – death, birth, marriage certificates just to name a few. 

Those documents and others do more than just provide supporting evidence for the event.  They provide a connection to the past.  Often the documents are signed – not just by the official whose job it was to do that, but by a relative for whom we’ve been searching.  That signature connects us to the document, not only to the event.  Take the Declaration of Intent for Levi S. Forman, signed in 1895, in Yiddish!  My vivid imagination now creates a mental image of my great-great grandfather with the red hair (how my grandmother used to refer to her grandfather) signing this important first step in attaining citizenship.