This format is important in one-pass posting, it is called once at the end of the program (instead of once per tool post).
This format is called once at the start of the program (instead of once per tool post). You will typically use this format to output many of the general startup codes which were previously left to Program Start.
This format is called immediately following the operation, loaded with state for the next operation on the current tool post. This format is used to turn things off from the operation which just ended, in a similar way to what would typically be done in Tool Change or Segment Start in multi-pass posting (such as checking <$*> reserved words to examine the previous operation). Those formats are not suitable for one-pass posting because they are called after the sync point (if one exists); for example it would be too late to output a coolant off code at that point.
This format is called once at each sync point specified by the user, and immediately after File Start. The wait code should be output here. This is also where global state decisions can be made (such as G600 codes for Citizen machines).