This move looks odd, as it develops a knight to a really odd square and to the edge, but it has some benefits:

This move puts opponents out of their comfort zone and they may get confused and make a mistake and a blunder and fall into a trap.

This move controls the f5 square, which white may use to start a kingside attack with the f-pawn, the g4 square, also if white is going for a kingside attack or an aggressive plan (such as putting the queen on g4 to attack the g7 pawn which attacks the rook that might be trapped), and the f7 square, safeguarding the king.

It doesn't look like 1...Nh6 actually develops a piece, however it can get closer to the center with Nf7, Nf5, Ng4, and sometimes even Ng8 to reroute the knight to f6 or e7.

1.f4 Nh6!?