When you decide to spend a day devoted to going onto old websites you used to use to delete all posts, updates, friends, and accounts.
You may decide to Internet Grave-rob because you are sick of that site, you have moved onto something else, or you don't want what you wrote years ago to come back to bite you in the butt.
Common feelings during IGR-ing are feelings of nostalgia, maybe happiness, depression, or laughing at how much of a general moron you used to be. All of these add to the reason why you should delete that crap.
I never use Myspace anymore, so I decided to IGR (Internet Grave-rob) it. It was quite rewarding.
Hey I'm bored, come over my house and we can go internet grave-robbing!