Why do states need to be concerned about laws passed in other states article and section?

The legal issues are more complex than a short reply can suggest, but if states acted independently, with complete autonomy, and with no obligation to recognize the rulings in other states, citizens would not be able to determine their rights and obligations when they crossed state lines. An important constitutional basis for the obligation to recognize the judicial proceedings in other states is in Article IV, section 1 of the U. S. Constitution, which binds all states to "full faith and credit" for judicial proceedings in all other states.