Pretty much, what this is where you get to select your starting point on solo mode. An example:
Before starting, they show you a map and you get to put your aircraft on the map wherever you want, at whatever speed and altitude you want.
This helps in many ways.
To do a descent, you don’t need to first ascend to a certain position
You can work on slow flight, cruising stalls, and emergency scenarios without having to fly to set them up.
It allows you to set up approaches to unique airports. 13/31 KLGA, KJFK, airports with sharp turns before landing. You start there and don’t have to take the somewhat unrealistic final/short final.
You may be asking, what if you don’t want to select your position, just keep it normal?
Simple! Just select the button on the menu that returns you to normal.
That’s incredibly unrealistic cos it just plonks you some distance from the runway. IRL, approaches vary and for example at JFK (because of all the buildings), you can’t have a direct approach.