Only just noticed this question. Thanks, Liam! I didn't know about the page tree on the Totara Help site. It is my preferred navigation method, so I was really missing it!
I often use the Table of Contents on the right-hand side and always wished there was something similar to access the other pages.
I'd prefer it if the page tree was expanded by default. It'd be good if the user could hide it, but it's not necessary (for me, at least). I personally hardly ever hide the page tree, but I like readjusting the width of it on platforms that allow it.