On: Very Short Reply Expected

[chmike]

Why do you want to hide that you red the message ? Is it when you would like to ignore the sender but are too curious and would like to know what message he sent you ?

[robryan → chmike]

Also because people that know you have read the message will sometimes expect a reply straight away or will think you are ignoring them.

[slig → robryan]

Exactly. Facebook knows that, and I imagine that's why they implemented this "receiver has read the message" as a way to pressure everyone to keep replying right away.