When you ask a friend to house-sit for you, there's an unspoken agreement between the two of you. You're saying, "I give you permission to fuck with my shit." Your friend/housesitter is saying, "I'm going to fuck with your shit."
While you're away, you get to imagine your friend rifling through your drawers, studying the labels in your medicine cabinet, and checking the top shelves of your closets. You want your friend to be interested in your life and the secrets it contains. When you get home, you search your friend's eyes for some hint that your friend knows more about you now. He might not speak of it, but he knows you better.
If you get the sense that your friend barely even gave a crap about you or your house while staying in it, you're disappointed. You want to believe that he made the most of his time in your home, which is why for redditor sosomething, this had to be a very satisfying note to come home to after his friend watched his house and dogs while he was away.
Glad you made yourself at home. Now get that penis looked at.