Only one X chromosome is required at any given time.  Additional X chromosomes (as in females) are inactivated in most cells except for gametes

The Y chromosome carries a number of critical genes required for spermatogenesis and sex development, but very few other genes.  Therefore, having two copies of the Y chromosome has minimal impact on the balance of gene expression

Dosage compensation requires that all excess chromosomes (i.e. 2 or more) are activated at all times during the cell cycle

The Y chromosome carries a number of critical genes involved in spermatogenesis and sex development.  Therefore, having two copies of the Y chromosome results in the overproduction of sperm and increased fertility