It will be extremely useful to directly draw and write down notes into the charts that come with every airport.
This will allow you to write down quick notes directly into approach plates, or when you get your taxi instructions, draw a line from your gate to the runway and have a quick reference.
The tool should come with an option to use a pen-like feature to draw, and include a highlighter option to highlight important areas. And an option to insert your own text into the plates.