How does NSFetchedResultsController and its delegate work?

As the question correctly says, I want to know how NSFetchedResultsController works and why use delegate methods instead of tableView.reloadData .

I am using them to build a TableView but it is not good at all, when loading the app it does not show me the entities in each cell and when adding a new entity, it is lagged and neither the lines of the cells

I leave the project in dropbox:

link

and a bit of the code below.

class TableViewController : UITableViewController, AddCourseViewControllerDelegate, NSFetchedResultsControllerDelegate {

    var managedObjectContext : NSManagedObjectContext!

    //Este objeto se encarga de integrar un fetchRequest con la ViewController.
    lazy var fetchedResultController : NSFetchedResultsController = {//Es un closure que devuelve un objeto.
        () -> NSFetchedResultsController in

        let fetch = NSFetchRequest()
        let entity = NSEntityDescription.entityForName("Course", inManagedObjectContext: self.managedObjectContext)
        let sort = NSSortDescriptor(key: "author", ascending: true)

        fetch.entity = entity
        fetch.sortDescriptors = [sort]

        let fetchedResult : NSFetchedResultsController = NSFetchedResultsController(fetchRequest: fetch, managedObjectContext: self.managedObjectContext, sectionNameKeyPath: "author", cacheName: nil)

        fetchedResult.delegate = self

        return fetchedResult
    }()

    override func viewDidLoad() {
        super.viewDidLoad()

        do {
            try fetchedResultController.performFetch()
        } catch {
            print("Error")
        }


    }

    func controllerWillChangeContent(controller: NSFetchedResultsController) {
        self.tableView.beginUpdates()
    }

    func controllerDidChangeContent(controller: NSFetchedResultsController) {
        self.tableView.endUpdates()
    }


    //Mark: - NSFetchedResultController delegate methods

    func controller(controller: NSFetchedResultsController, didChangeObject anObject: AnyObject, atIndexPath indexPath: NSIndexPath?, forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath?) {
        switch type {
        case .Delete:
            tableView.deleteRowsAtIndexPaths([indexPath!], withRowAnimation: .Fade)
            break;
        case .Insert:
            tableView.insertRowsAtIndexPaths([newIndexPath!], withRowAnimation: .Fade)
                break;
        case .Move:
            tableView.moveRowAtIndexPath(indexPath!, toIndexPath: newIndexPath!)
                break;
        case .Update:
            let curso = controller.objectAtIndexPath(indexPath!) as! Course
            let cell = tableView.cellForRowAtIndexPath(indexPath!)
            cell?.textLabel?.text = curso.title
            cell?.detailTextLabel?.text = curso.author
                break;
        }

    }

    func controller(controller: NSFetchedResultsController, didChangeSection sectionInfo: NSFetchedResultsSectionInfo, atIndex sectionIndex: Int, forChangeType type: NSFetchedResultsChangeType) {

        switch type {
        case .Insert:
            let set = NSIndexSet(index: sectionIndex)
            tableView.insertSections(set, withRowAnimation: .Fade)
            break;
        case .Delete:
            let set = NSIndexSet(index: sectionIndex)
            tableView.deleteSections(set, withRowAnimation: .Fade)
            break;
        default:
            break;
        }



    }

    //MARK: - TableView dataSource

    override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
        return fetchedResultController.sections!.count
    }

    override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return fetchedResultController.sections![section].numberOfObjects
    }

    override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCellWithIdentifier("Cell")!

        let course : Course = (fetchedResultController.fetchedObjects![indexPath.row]) as! Course

        cell.textLabel!.text = course.title
        cell.detailTextLabel!.text = course.author

        return cell
    }


    private func getFetchedController() -> NSFetchedResultsController {
        let fetch = NSFetchRequest()
        let entity = NSEntityDescription.entityForName("Course", inManagedObjectContext: self.managedObjectContext)
        let sort = NSSortDescriptor(key: "author", ascending: true)

        fetch.entity = entity
        fetch.sortDescriptors = [sort]

        let fetchedResult = NSFetchedResultsController(fetchRequest: fetch, managedObjectContext: self.managedObjectContext, sectionNameKeyPath: "author", cacheName: nil)

        return fetchedResult
    }


    //MARK: - AddCourseDelegate

    func addCourseViewControllerDidSave() {
        do {
            try managedObjectContext.save()
        } catch {
            print("Error al guardar el curso.")
        }
        self.dismissViewControllerAnimated(true, completion: nil)
    }

    func addCourseViewControllerDidCancel(curso : Course) {
        managedObjectContext.deleteObject(curso)
        self.dismissViewControllerAnimated(true, completion: nil)
    }


    //MARK: - Segue way

    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        if segue.identifier == "addCourseSegue" {
            let nextVc = segue.destinationViewController as! AddCourseViewController
            nextVc.delegate = self

            let selectedCourse = NSEntityDescription.insertNewObjectForEntityForName("Course", inManagedObjectContext: managedObjectContext) as! Course
            nextVc.course = selectedCourse

        }
    }


}