When you are doing a Ph.D. then dissertations are a must-to-do part of your education. Every educational institute has its methods of checking its students. Though if you are British and you buy dissertation UK-formatted then there are high chances that you may get a doctorate. I think that dissertations are necessary for completing your Ph.D. as knowing how to write or do dissertations is taught in all Ph.D. programs. There is no chance that your teacher may pass you without submitting a dissertation but if it happens, you are lucky enough.