Does anyone know of a situation where it would be advantageous to promote to a knight instead of queen. I suppose it might be possible to have a situation where promoting to Knight would cause check mate. Just curious.

The other main reason for underpromotion is where promoting to a queen would result in stalemate.

I´ve onced promoted to a bishop to deliver checkmate.

Mostly because I didn't have any queen or spare rook to place upside down.

Not that this answers your question though.

U cant be bothered to type this out in puzzle format, Mate in 4

The MOTHER of all underpromotion tasks. Black promotes to a Queen White has to promote to a Queen, Black promotes to a Rook, White has to promote to a Rook, Black promotes to a Bishop, White has to promote to a Bishop, Black promotes to a Knight, White has to promote to a Knight.

1. L. Yarosh, Shakhmaty v SSSR, March 1983

Mate in 4

1.Rxh4 cxb1Q 2.axb8Q Qxb2 3.Qb3 Qc3 4.Qxc3# Qe4 3.Qxf4 Qxf4 4.Rxf4# cxb1R 2.axb8Q? Rxb2 3.Qb3 stalemate 2.axb8R! Rxb2 3.Rb3 Kxc4 4.Rxf4# cxb1B 2.axb8Q? Be4 3.Qxf4 stalemate 2.axb8B! Be4 3.Bxf4 Bxh1 4.Be3# cxb1N 2.axb8Q? Nxd2 and no mate 2.axb8N! Nxd2 3.Nc6+ Kc3 4.Rc1#

Notes:
14 + 8 = 22 pieces
key: takes Knight, creates pin, provides for checks
flight squares before/after key: 0/0
Black, White moves/captures to promote: capture - capture



Underpromotion
motivations:     Black                    White
Rook             flight creating selfpin  unguarding flight square
Bishop           anticipatory selfpin     pin avoidance
Knight           flight creating capture  takes flights

The first direct-mate Babson Task.

Sometimes in r v. p endgames, promoting to a knight with check staves off a mate in one.

Yes, usually to give check.  A much more difficult problem is a reason why you would want to promote to a bishop...

Nice!