Why does computer suggest [h4]?

White to move.

Why does computer suggest [h4]?

Outpost for Nf3? or to ruin black king's house?

Your bishops, f3 knight, queen are all pointing to blacks kingside.  

After Ng3 you now have the other knight on the kingside.  

You have central control, and space with the pawns on d4-e5.

Blacks lacks a knight on f6 to help defend the king.

h4 is a common theme to open up the kigside.

...also your control of the center and the advanced e-pawn will make it difficult for Black to get his Queen side pieces into the fight on the King side.

Thank you for explanation

Now I understand that white can open up black's kingside by proceeding a pawn to h4, h5.

(also make use of white's minor pieces to attack black king)