This emoji is a more accepted way of showing tiredness or sleepiness rather than the Sleepy Face emoji. Just the face alone should be enough to let your recipient know that you are feeling tired. Your friend invites you out for drinks but you have had a long and tiring day at work, you could politely decline with the face followed by some complimentary text. This emoji could also be used to show that you find something boring or if you want to throw shade at a person's topic of discussion. Let’s say your friend starts talking about their collection of rice grains; they have yammed on about the subject in the past for a long time. You could stop the conversation in its tracks (and also have an angry friend on your hand) if you respond: Oh this again 😴

Sleeping Face was approved as part of Unicode 6.1 and later added to Emoji 1.0 - this update also saw Grimacing Face and Hushed Face join the party.