Disable order processing email for virtual products only in WooCommerce on child sites.
Snippet Type
Execute on Child Sites
Snippet
add_action( 'woocommerce_checkout_process', 'wc_custom_checkout_process_for_virtual_products' );
function wc_custom_checkout_process_for_virtual_products() {
    // Check if the cart contains virtual products only
    $virtual_products_only = true;
    foreach ( WC()->cart->get_cart() as $cart_item_key => $cart_item ) {
        if ( ! $cart_item['data']->is_virtual() ) {
            $virtual_products_only = false;
            break;
        }
    }
    // If the cart contains virtual products only, remove email notifications
    if ( $virtual_products_only ) {
        add_action( 'woocommerce_email', 'unhook_those_pesky_emails' );
        function unhook_those_pesky_emails( $email_class ) {
            remove_action( 'woocommerce_order_status_pending_to_processing_notification', array( $email_class->emails['WC_Email_New_Order'], 'trigger' ) );
            remove_action( 'woocommerce_order_status_pending_to_processing_notification', array( $email_class->emails['WC_Email_Customer_Processing_Order'], 'trigger' ) );
        }
    }
}