Think of Docs as a sheet of paper, you can put what you like on there and display it how you want. It doesn’t really “do” anything with your content so is best used for text based planning that is often long or contains many links. A google doc is like a book so it is as short or as long as you want it, you can even add a table of contents to make navigation easier.
Unit plans and group plans are my top planning tasks I use docs for. Adding links out to learning content ready for a lesson, making notes on student achievement and duplicating (you can’t have multiple tabs like in sheets) for each unit or group is what I love most.