This is usually done to advertise traits which when put in the direct form of a status update would make the poster's motives far too transparent.
MARK: She probably wants everyone to think she's the type of girl who is tight with her friends, and people would call her on it if it were a status update.
KATE: A proxy wallpost? Seriously?
"We had such a great time last week! I miss you so much <3"
Soon, everyone you know will see it in their feed. And, unlike a status, no one will call you on it for fear of you playing the None Of Your Business card.