Scandinavian 2...h5

This is an idea to bring the rook out early.

1.e4 d5

2.exd5 h5

Now if white plays 3.Nc3 or 3.c4, black can play 3...Rh6

If white plays 3.d4 then black can play 3...Qxd5

And how would you benefit from this?

If you bring the rook out it will be chased around and you have a damaged king side. If white plays d4 you get the same as normal scandinavian but then with a loss of tempo and a damaged king side.

The point is that the strenght of a piece revolves around various factors, and among them there is the moment of the game. A rook is not very powerful in the early moves. It's easily attacked and chased around the board. It lacks open lines to work with. An example is that winning rook+pawn for bishop+knight in the opening(it's often possible with an attack against f2/f7 with a castled opponent king) is usually a bad idea. 2...h5 likely gives your opponent an edge in development(wasted tempo+moves gained while attacking the rook) and weakens your king position.This is not compensated by the active rook, since at this stage it has not a great strenght. As a consequence the variation is not recommended.