You may want to restrict certain HR users from seeing employees at a certain job level, for example company directors. To do so you can create job role levels by going to:

Administration -> HR -> Data Management -> Job Roles

then select the option at the bottom labelled 'job role levels':

Once you're on the job role level page just click Add to create a new job role level. Once you have your job role levels made you can edit a job role by clicking Actions -> Edit and then select the applicable job role level:

Once you've added your job role levels and then assigned them to the correct job roles navigate into

People -> Users

locate the HR users you want to restrict and click Actions -> Edit then scroll down to the 'restrict access to job level(s) section and simply tick the job role levels you'd like the users to have visibility of:
 

Once you're happy with the selection click Submit and your users will now only be able to see the job role levels selected.