instancetype is an Objective C keyword that is meant to be used as a method return type representing the type of the current (sub)class. Generally, you'd want to use it in constructor-type methods. It's preferable to returning id or the specific class so that it works nicely without requiring casting or giving up type-checking. E.g.

@interface MyClass : NSObject
+ (MyClass)myClassWithValue1:(NSString*)aString;
+ (id)myClassWithValue2:(NSString*)aString;
+ (instancetype)myClassWithValue3:(NSString*)aString;
@end

@interface MySubClass : MyClass
@end

If you call +myClassWithValue1: when working with MySubClass, you'd need to cast it back to MySubClass. If you use myClassWithValue2:, you loose type checking. If you use myClassWithValue3, you get the best of both worlds.

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