Recently, I encountered a reason to be wary about create shared Excel spreadsheets when one ballooned in size. It ended up growing to around 130 megabytes before I tried turning off sharing to see what happened and the size shrunk to under 200 kilobytes. From this, it would appear that the version control information was the cause of the explosion in file size. With that in mind, I set about to looking through the settings to see if there were any that might need optimisation. The default action is to keep thirty days of change tracking but I have this reduced to a single day in order not to be keeping too much. Quite how much, you need to retain is up to you but I will keeping an eye on things now that I have done this.