Q:

IBOutlet and IBAction

What is the purpose of using IBOutlets and IBActions in Xcode and Interface Builder?
Does it make any difference if I don't use IBOutlets and IBActions?

Swift:
@IBOutlet weak var textField: UITextField!

@IBAction func buttonPressed(_ sender: Any) { /* ... */ }

Objective-C:
@property (nonatomic, weak) IBOutlet UITextField *textField;

- (IBAction)buttonPressed:(id)sender { /* ... */ }

A:

IBAction and IBOutlet are macros defined to denote variables and methods that can be referred to in Interface Builder.
IBAction resolves to void and IBOutlet resolves to nothing, but they signify to Xcode and Interface builder that these variables and methods can be used in Interface builder to link UI elements to your code.
If you're not going to be using Interface Builder at all, then you don't need them in your code, but if you are going to use it, then you need to specify IBAction for methods that will be used in IB and IBOutlet for objects that will be used in IB.

A:

The traditional way to flag a method so that it will appear in Interface Builder, and you can drag a connection to it, has been to make the method return type IBAction.  However, if you make your method void, instead (IBAction is #define'd to be void), and provide an (id) argument, the method is still visible.  This provides extra flexibility, al  
All 3 of these are visible from Interface Builder:
-(void) someMethod1:(id) sender; 
-(IBAction) someMethod2; 
-(IBAction) someMethod3:(id) sender;

See Apple's Interface Builder User Guide for details, particularly the section entitled Xcode Integration.

A:

You need to use IBOutlet and IBAction if you are using interface builder (hence the IB prefix) for your GUI components.  IBOutlet is needed to associate properties in your application with components in IB, and IBAction is used to allow your methods to be associated with actions in IB.  
For example, suppose you define a button and label in IB.  To dynamically change the value of the label by pushing the button, you will define an action and property in your app similar to:
UILabel IBOutlet *myLabel;
- (IBAction)pushme:(id)sender;

Then in IB you would connect myLabel with the label and connect the pushme method with the button.  You need IBAction and IBOutlet for these connections to exist in IB.

