International (non-EU) students must apply for a Tier 4 (General) Student visa in order to study at a UK university. The general (common) reasons for a visa refusal seem to be showing incorrect documents, having insufficient funds or a suspect immigration history, amongst others.
What about smaller issues, like submitting a passport photo that's older than 1 month? Or having a course title on the application form that differs from that in the CAS by one word? Are these issues serious enough to warrant a visa refusal or not?
From De Montfort University FAQ section:
Why could my visa application be refused?
Prior to refusing your visa application, the UKVI will have assessed all the information you have provided with your visa application and any information they have regarding your immigration history, and decided that you did not meet the requirements of having a valid CAS, sufficient maintenance or for other reasons such as your immigration history. You will be issued with a notice of refusal of entry clearance which will state the full reason your visa application was unsuccessful.