Even if your settings are set to show what you post to only your friends it is still possible for an employer/prospective employer to view what you have posted on Facebook. They don't have to "hack" your account.https://www.facebook.com/help/282207828490074/
If someone else tagged you in a photo, the employer/prospective employer will be able to see it. Would you want the photo of you acting stupid to be seen by them?
If you post something and someone else shares it, it can be seen if the other person allows anyone to see his/her activity on Facebook.
They may be able to see comments YOU made on other people’s photos and wall. If it is something negative, you can kiss that job goodbye.
Bottom line: a good recruiter will be able to find out what you post on social media without "hacking" into your account.