Female XX genotype gives advantage for genetic disorders?

[SysBio]

Hello,

I have read that since females have an XX genotype, they have an advantage over males' XY genotype for some genetic disorders.

If the female has a recessive allele on one X chromosome it may be covered by a dominant allele on the other X chromosome....but in males, any recessive allele on the X chromosome would be expressed.

But, I also read that in females, one of the X chromosomes becomes deactivated into a BARR BODY

How does a female have any genetic advantage if one of the X chromosomes becomes deactivated into a Barr Body?

[JackBean]

My guess would be because it is not deactivated uniquely and uniformly throughout the body