Travelling between different places in a solar system takes time. Sometimes it will even be faster to make a micro (in-system) jump than using the M-drive.
When jumping to a system, it might be important to know where to get free fuel. If you have a cargo or passengers for the main planet, then it might not be economical to go to a gas giant (to get free fuel) in the outer system as well. Even if the main planet has oceans, you might not be allowed to refuel in these. If you don’t have any cargo or passengers or any other business to the main planet, then you might want to jump directly to the gas giant instead. There you can refuel and jump to the next destination.
How can you plot all the relevant information for a system in a hex on the subsector map? My idea is to divide the hex in six triangles, and show the most important planets with the important moons in each triangle. If there aren’t enough important planets, just leave some triangles empty. But as a minimum 2-3 triangles should have planets. I have put the gas giants in the right part of the hex, just like where the gas giant icon is usually placed.
This is my example for the Terra system. What do you think?