Initially hide the USPS fallback rate if the user didn't enter a state or postal code.

woocommerce-hide-usps-fallback-rate

/**
 * Returns either true or false depending on whether the user has entered
 * a shipping state or postal code.
 * 
 * @param none
 * 
 * @return bool
 */
function initially_hide_usps_fallback_rate() {

	if ( ! WC()->customer->get_shipping_state() || ! WC()->customer->get_shipping_postcode() ) {
		return true;
	}
	else {
		return false;
	}

}

add_filter( 'woocommerce_package_rates', 'hide_shipping_if_address_not_entered', 999, 2 );
/**
 * USPS has an option for a fallback price, but it shows it before the user even
 * enters their address.  This fixes that by checking whether the user
 * has entered any location information.  If not, we unset the USPS rate.
 * 
 * @param $rates
 * @param $package
 *
 * @return mixed
 */
function hide_shipping_if_address_not_entered( $rates, $package ) {

	if ( initially_hide_usps_fallback_rate() ) {
		unset( $rates['usps_fallback'] );
	}

	return $rates;
	
}