What happens if someone actually tries to delete their past facebook activity to hide it from friends, colleagues, and employers?
How tiresome is it do delete your facebook activity? In short: very tiresome! Jennifer Golbeck from Slate magazine tried that experiment and found it very exhausting to do it by hand. But there are also scripts for your webbrowser that can do the job.
Note that this will only hide old posts from your ‘audience’ but neither from Facebook nor the NSA.