It all depends on the amount of competition you are up against. Put yourself in the place of the employer, who will be looking for a number of qualities in the candidates they are interviewing. One of those characteristics will be how clever or hard working they are. The person with a distinction will naturally be presumed to be either more intelligent or hard working than the candidate without one. They will look at other factors, but the person with the distinction has the advantage. You may be entering a field with very little competition or where other candidates do not have a Masters degree, in that case a distinction will be less important.