That is one application, another application of Fast Post is when looking at a complex pulse signal and the interest lies in any ringing, noise, or slope deterioration of the pulse edges. For example, the fuel injector current signal rise time can be expanded to see when the actual injector pintle opens up (due to counter EMF caused by the pintle motion). When the injector pintle closes a similar glitch can be seen on the waveform. In this application, you would want a Fast Post so the waveform can be expanded horizontally as much as possible (with fast refresh rate for real-time viewing) and use the Trig Pos to place all of the expanded pulse on the screen in real-time.
In the current firmware version I can slide the Trig Pos to the left and leave it there for real-time waveform viewing without having to stop acquisitions. Now I can view the expanded Fast Post waveform in great detail at real-time fast update rates.
Although I mentioned the automotive application, there are many other uses where Fast Post would enable more accurate pulse width adjustments and also provide for better viewing of complex pulse irregularities in real-time with a fast refresh rate.
For off-line viewing of the captured XML files, the Fast Post XML file will not waste buffer space (sequence numbers) on information that is not desired. Instead, twice as much desired information post trigger will be available for examination.
Hope this serves to demonstrate why I think the Fast Post feature is important.
As you mentioned in previous posts, for Fast Post, the firmware could pre-position the Trig Pos near the left side of the display and then the user could fine adjust as required.