Purpose of Instance Methods vs. Class Methods in Objective-C

I have checked out all these questions...

• Difference Class and Instance Methods
• Difference between class methods and instance methods?
• What is the difference between class and instance methods?

...and all they explain is how instance methods are used on instances of a class and class methods are used with the class, when a message is sent to a class. This is helpful, but I'm curious to know why one would use a class method vs. an instance method.