Respawning
Black out and you wake up in your bed, or back home on your starting world if you don't have one.
When your Health hits zero you black out and come round with every bar full. A Bed is how you choose where that is. Without one, every death sends you back to the same spot on your home world.
If your bed is on a world in another star system, you can't get back to it, and you'll respawn at home instead.