To be considered 'low risk', you must already be in the UK or applying for a Student Route visa in your home country.
If you are from a low risk country you are not required to submit some of your documents with your application. You will still need to have your documents available because UKVI can request them from you at any point during the application process. The IST will not provide you with a CAS until you have demonstrated that you have these documents available to you.
If you have an in person appointment with the UKVI you must take all your orginal documents with you.
Please check below if you are from a 'low risk' country:
Low risk country list