If you aren't terribly fond of emoji, you're not alone. There are those who even find them distasteful or disrespectful, arguing that their status as informal shorthand disqualifies them from "real" communication. The facts, however, seem to point in the opposite direction. Nobody knows when the first :) smiley-face icon appeared in text. The colon and parentheses are very old symbols in language, dating back to long before modern computers were even a thought. A wider variety of emoticons began to crop up in Japan in the early 1990s, leading us, eventually, to the wide range of emoji that we have today. Emoji as we know them know look very lifelike and include a range of diverse skin tones, realistic-looking facial features and even inanimate objects. While many argue that the use of emoji hampers proper communication and impairs the ability to self-express, they actually fulfill a very human need that text alone cannot; the need to convey emotion.
A series of exclamation points after a sentence in all capital letters denotes some sort of intense excitement, but without proper context, you won't know if your friend is excited that Green Day is in town and are stoked for the show, of if they're angry that the band is in town and they can't go see them for whatever reason. While a voice call or video call, or even a selfie accompanying the text, is always an option, it's nowhere near as quick and convenient as a few taps on a keyboard. If those taps can convey the same emotion as a picture through the magic of emoji, that makes things that much easier. Trying to communicate the same emotions by text alone can be tricky and counter-intuitive. "I'm so happy you made time to come and visit.", while sincere, seems utterly dry when read on a page or a screen. To spice it up, not to mention reveal whether the expression is sarcastic or not, would require one of two things; additional types of stimuli, or a good amount of additional text. In a world where people have a hard time even finding the downtime for proper sleep, two seconds to grab an emoji from a list instead of thirty seconds to type some context for your message can really add up.
It's not just a matter of convenience, of course; emoji are the closest thing to human body language that can be rendered in text. There are many situations besides being strapped for time that can cause somebody to want to communicate as much as possible in the strict context of text, and emoji open up a whole new world of communication in that context. With emoji, somebody who couldn't communicate certain things before is suddenly as expressive as somebody standing face to face with you, speaking out loud. Lovers separated by nations, who would have to avoid using data as much as possible, can use emoji to communicate their affection in ways normally reserved for pictures and video, such as smiles and hearts, speaking with cartoony pictures what the human eye normally picks up from another human face. Those who can't communicate normally, such as cerebral palsy patients, suddenly have access to the full spectrum of body language in their communications.
With the advantages of being concise, convenient and universally expressive on their side, it's not hard to see why emoji have caught on and become a worldwide phenomenon. Somebody in America who doesn't speak a word of French could receive an emoji from a user in Paris and connect with them instantly. Somebody who's posting on Twitter and doesn't want to upload a selfie just to punctuate a Tweet can use an emoji. The number of use cases for emoji are about as vast as the ever-growing selection of them.