Disabling GST for your business will change your columns' Tax Types to Non-GST. This will result in GST amounts not showing on your reports for historical records that have attracted GST. 

It will also stop the ability to complete BAS and GST reports. 

It is highly recommended that you finalise your GST reporting and ATO submissions before setting this file to Not Registered. You should speak with your accountant before switching off GST Registered.