@Jerry As Lukhnos pointed out, Cocoa developers prefer to use delegates pattern in situations where others might create a subclass and start overriding methods.

Objective-C's largest strength is arguably its dynamism, and in most cases, delegates allow for greater dynamism. Class hierarchies have rigid structures, which can cause problems in complex systems. Delegates, on the other hand, are flexible, and can even be changed at runtime. There are many tools in other languages to deal with these kinds of problems (e.g. multiple inheritance) which become unnecessary when using delegates.