You would typically use five axes for complex parts unless there was a compelling reason not to. Interestingly, as I am buying one at the moment (our first) I had a chance to talk to different machine shops about their different brands here in China. They alleged that foreign dual use export restrictions have resulted in a situation where China's local five axis machines are now both cheaper and more accurate than the available foreign imports (source: major prototyping shop, machine count >20, machine brands 3x, 5 axis count 10+). This was supported by the second shop I visited who also said they will no longer buy imports.