The Boolean skills should be used when you are looking for a job where this ability is essential. When you are specifying a number of required skills, our system will look for candidates who have mentioned all of those skills (AND) or non of the skills you selected (NOT).
But be careful with the use of Boolean! It might be that candidates have the required skills but have not mention them specifically on a public network and therefore you can not see their profile. Therefore we recommend to use the Killerquestion to check if the candidates have the required skills you are looking for.