It depends.  In some cases (some universities, some courses) it is considered desirable, if not essential; in others, it is not needed.  To be certain, you should check the requirements of the course you are applying to at each of your university choices.  You should also check general university requirements of the university if there are any.  It is important that you do not waste a university choice so email the university if you are in doubt.

Alison Patterson