What does this gain you beyond what you can already do in a debugger? Writing Mac apps in Objective-C I got really used to just setting a breakpoint in the cod

What does this gain you beyond what you can already do in a debugger? Writing Mac apps in Objective-C I got really used to just setting a breakpoint in the code in question and in gdb calling methods and even replacing variables with the output of method calls, which covers everything he seems to be doing in the sample on his page...