"Using ajax for every click creates extra unnecessary load on the server, we have 1000's of students and if they were all on a subject that was using collapsed topics, every time each one of them click on a collapsed topic it would send an ajax request to the server creating lots of overhead. Is there a way you can make the server side stuff optional, or even turn off?"
The ability to turn off has been implemented. However, to reduce server load the web browser could be instructed to only update the state of the toggles when the user moves away from the course. This would be achieved through the use of an event such as 'onunload' or 'onbeforeunload'. However current browser support differs for these events and is not consistent. Therefore time needs to pass until a consistent method is determined, the events are fully supported by all or an alternative suggestion is provided.