My company does a lot of true-crime TV stuff and my bosses struggle a lot with re-enactments. They constantly ask themselves if the audience needs it, but ultimately it comes down to the network sending back notes saying "where is recre?" and not wanting a battle.
It's difficult and above my pay-grade, but it's a fine line between needing them or not and as much as you want to trust your audience, it seems the public responds to it based on testing. We talk about the classic documenataries like The Thin Blue Line where most felt it works (Touching the Void comes up a lot too, the "performances" in that are great) and have said documentary isn't the best title for it- docu-drama or non-fiction seems to fit it more. For me as a viewer, it all depends how it compliments what I'm seeing and hearing, but I'm certainly biased from being exposed to it daily.
EDIT: Sorry if I'm taking away from any discussion, just saying that I find from my own perspective it stems a lot from the filmmaker(s) wanting to convey intent and meaning behind the information in the best way. So it stems more from asking if something narrated or archival doesn't work then is this the best way to convey information? That being said, there is a trend to try to make it FLASHY and MOODY, but audiences seem to like that cinematic aspect to it.