If you are in a vacancy and you use the clone button, it will create a new vacancy and copy over all the details from the top half of the vacancies screen (bar the entered date and the consultant). It will also copy the jobsite comment and the skills for that job. 
This is useful for the following examples:

1. You have 2 roles a junior and a senior - you will only have to change the job title, salaries and the skills experience
2. The company have had the exact same job in the past and the position has reopened.