Here is one small example of something that won't be apparent to someone without a demonstration.

Say I have a class called Foo and I realise, as I'm using it, that I want to add a method called doSomethingElse, I can just type the new method call and have appCode create the method for me. Ie:

Foo *foo = [[Foo alloc] init];

[foo doSomething];

[foo doSomethingElse]

doSomethingElse would be marked in red. I just have to hit command-enter, select 'Create method' and appCode creates the method signature in Foo.h, creates the method in Foo.m and puts the cursor in the body of the method ready to implement it.

This improves coding flow remarkably.