For example, here's what Emojipedia writes about the " " (tongue) emoji: "A tongue, sticking out. May be used as a childish sign of defiance. Alternatively: licking, in various contexts." ...

It's more chit-chatty and friendly than email; plus it makes emoji at work acceptable. Using emoji in work emails may look unprofessional. On Slack, however -- no such problem. "It's weird ...