Useless Delays

As I was racing through simple checkmate exercises near the beginning of John Nunn, 1001 Deadly Checkmates (2011), one created slight difficulty.

White to move

I found 1.Qa8+ Kd7 2.Nc5# almost instantly, but Black can interpose with 1...Rb8, making the exercise checkmate in three. I spent a long time trying to find something that was not there because all of the exercises in the first section are mate in one or two. Finally, I peeked at the solution to see what I overlooked.

I was warned in the introduction:

[R]eaders should be aware that in some cases the defender can delay mate by "spite checks" (giving away pieces with check) or by interposing pieces that can just be taken. In most cases I don't mention such pointless delaying tactics. (7)

Cyrus Lakdawala takes a different approach in Tactical Training (2021). This position is presented as a mate in six.

White to move

The game finished with 24.Qxh7+ Kxh7 25.Rd4 and Black resigned. Black can delay the inevitable checkmate with a knight interposition on e4, a queen sacrifice on h3, and a rook sacrifice on c4. These useless delays change nothing, but they are listed in Lakdawala's solution. He also uses the game's move numbers rather than beginning with 1, as Nunn does in 1001 Deadly Checkmates.

In "The Spite Check" (2020) on ChessBase.com, Karsten Müller presents a "spite check" as provoking an error.

White to move

After 62...Ne3+

As Müller notes, only 63.Kh5 wins. White played 63.Kf3 and went on to lose. Here, however, the "spite check" does not delay an otherwise unstoppable checkmate, but the advance of a pawn that is otherwise certain to promote. By reacting incorrectly to the check, White allowed Black's knight to reposition to a square where it can move to stop the pawn. Meanwhile, Black's passed c-pawn remains a threat.

Müller's use of the term "spite check" suggests that delaying tactics might have a secondary purpose in some instances.
 
I posted this position from my reading on Facebook yesterday.

White to move

White has a forced checkmate in six, but many who saw it thought they found a checkmate in three. If you found the first move and the reason the sacrifice works, does it matter how many delaying moves Black can throw in the way?