The short version: machete order means watching the first two episodes of the original trilogy. Then, after Darth Vadar drops his bombshell on Luke, watching episodes II and III or the prequels. This explains the back story - how Vadar came to be Luke's father. Then it follows that up with the final episode of the original trilogy, which is the conclusion of Luke's hero journey. Episode I is skipped on the grounds that it sucks, and that it is superfluous.
The main argument for machete order is that no one cars about the characters in the original trilogy. People do care about Luke. So treat the original trilogy for what it should be: Vadar's back story.