Unless you've got a nasty icky bug hidden somewhere in 10,000+ lines of code and have to dig it out. That not fun.
Even more fun is a memory corruption bug hiding in someone else's crappy, asynchronous, threaded 10,000+ loc GUI components which are messy extensions of an external company's crappy, asynchronous, threaded 100,000+ loc GUI components, and the bug has a 0% chance of showing up with the debugger enabled.
Aaargh...
Yes, I just had a bad couple of days at work.