Black mold can kill you if you already have breathing problems or you're very young or very old.
It's still not a good thing to breathe in black mold spores or live in a house where mold including black mold is hanging around and growing.
If you do have black mold in your house it needs to be taken care of because not only does the black mold look bad it can also cause health issues in some people.
Any type of mold should be gotten rid off using bleach or something else to kill the mold.
If the mold is in drywall you should cut out the moldy drywall and clean behind the wall and then replace the moldy drywall with fresh new drywall.
Bathrooms are more prone to getting mold including black mold due to the high moisture content in the bathroom.
Using a vent van to help draw out moisture can help keep the mold from happening.