When shooting a combination shot in pool, many players work backwards from the pocket (hole). if I want the 3 to go into that corner, i need it heading in the direction of the hole. To get it going in the direction of the hole I need to hit it with the 5 in a certain spot. To get the 5 to that spot I need the white cue ball hit in a certain direction, etc.
How does this translate to planning a line through a track? You can think of it the same way! Work backwards from where you want to be pointed and see where you need to be in the turn before to set up for it.
In this example I want to maximize drive for the straight after the turn marked "1". Working backwards from that, I can apply the following process (note, this is not a track I know, nor is it necessarily "correct" just an example of how you can think about a set of turns).
To drive out of 1, I may want to apex late, which means a late turn-in for that turn (point 2)
To get there I need to exit the previous corner but end up to the left side. So at point 3, I need to make more of a turn than the track does which may mean an early apex without getting on the power too much
Since 3 is not a fast exit, i can drive into it directly from 4 and not use the whole track to the right (since i'd just be wasting distance)
Since I don't need a huge drive out of 4, i may want to double-apex that turn at 4/5.
if I know i can double apex 4/5 I can carry a lot of speed into 5.
This is just an illustration of a thought process. Probably not the fastest way around this track (wherever it is). Looking at it in the real world would probably show something different, but working backwards from an obvious goal (in this case drive out of 1...) may show a different approach for the prior corners causing some to be throwaways and others to be worked backwards. There may also be a variation based on what kind of lap you're doing. If you're setting up a qualifiying flyer, you may want to treat the whole lap before as a "throwaway" just to get a higher speed at the start line.