The exclusionary rule is used to keep out evidence that was illegally obtained. This usually occurs when law enforcement searches or seizes something without a warrant and an exception does not apply.
However, the evidence will not be suppressed if the good-faith exception applies. This exception comes into play when law enforcement acted with an objectively reasonable good faith belief and they acted lawfully.
Usually this is a last resort for the State to try and prevent suppression after exhausting all remedies. The South Carolina Supreme Court recently upheld the good-faith exception first and determined that it wasn't necessary to go through the other exceptions and see if they applied: