I didn't revise for any of my mocks, which did result in me getting D's, E's and even U's in some cases. I also found that I didn't have time but when it came to my real exams I revised and got all A's and B's
For sixth forms you might need to show your report which will have your predicted grades, your mocks will impact these slightly but not horrible.
Good luck when it comes to the real exams and your course work!