To start, it is good netiquette to use emoticons. But, in moderation. Given, they annoy some people.
So, happy emotions are fun to share. Then, we share happiness. It follows, emotions. Thus, slightly different expressions.
Emoticons annoy some. Teens made their use popular. It is appropriate to use an emoticon if you are just kidding or writing something sarcastic. It is inappropriate to use an emoticon for professional communication because professional communication is serious.