The Origins of Wonder
This fanning method can be exploited in various ways. It's earliest use was probably to create an illusion that the faces of the cards in the deck were blank. A blank-faced card was placed on the face of the deck before it was reverse fanned. See Walter Gibson's “The Appearing Spots” in The Sphinx, Vol. 23 No. 2, Apr. 1924, p. 60.
To force a card on an impromptu stooge with a Reverse Fan, see Force with a Reverse Fan and also Card Divination by Spectator, Using Fake Index in Reverse Fan.
The precursor to this idea was to hide a face-up card in a traditional fan, simply shielding the exposed index from view. Harry Hanaoka contributed this idea to The Sphinx, Vol. 26 No. 10, Dec. 1927, p. 366. Oddly, Hanaoka suggests that only court cards are capable of being hidden in the spread due to their border, even though number cards share that same amount of white space around their edges.
Using a reverse fan, however, naturally swaps the side of the cards being displayed. This causes the indices of any face-up cards to be hidden beneath the card above it. Judson Brown exploited this feature to create an Automatic Shuffler effect in which every other card turns face up in a deck that has just been shown face down. See the final notes in the “Pressure Fan” description in the posthumously published Page Wright's Notebook, 1991 (written ca. 1929), p. 147.
In Ed Marlo's “Separating Aces (4th method)”, Ibidem, No. 8, Dec. 1956, p. 141 of the book edition, cards have to be inserted into a deck with secretly reversed and distributed Aces. It says to simply push them in, and in brackets this note is given: “Or insert into a reverse fan—Aces cannot show.” Marlo later expanded on this principle in Jon Racherbaumer's Hierophant, No. 4, summer 1970, p. 210, in his contribution “right-hand pressure fan notes”, where he applies the idea to All Backs and Triumph effects.
David Regal used distributed, reversed cards in a face-down Reverse Fan as key cards, allowing specific placement of cards that are inserted into the fan; see “Clandestine Collections” in Close-up & Personal, 1999, p. 18.