The Force is so weak with this lot!
Superfetch attempts to predict what you are about to do and preloads files in to RAM. Prefetch loads critical information in about files to attempt to make them load faster. Between the two, they significantly improve loading speed including startup. The problem with them of course is that they consume CPU power, RAM and are loading things in to RAM all the time that you may not use. Another issue is that they may not be able to predict what you are about to do, if, for example, you are going to a new level in a game and loading in a map that the computer hasn't seen before.
Some users elect to disable the Superfetch and Prefetch once they have an SSD to stop wasting RAM and CPU power and cut down on unnecessary disk reads. Thing is that if you don't disable them then many loading times will be almost the same for SATA as they are for PCIe because you aren't directly comparing the speed of the two drives because Superfetch and Prefetch are undermining the results.
The only way I can understand that people can't notice a difference is because they haven't disabled Superfetch and Prefetch. To me there is a vast and very noticeable difference! Either that or I am the only Jedi in the universe, which seems pretty unlikely. Possible, though! *thinks* Nah, REALLY unlikely.