It kind of depends on the person. I used to use them a lot because it's difficult to express the mood of the sentence you're typing when all you use is written word :(. See what I did there? yeah...I'm amazing
they are called emoticons because they express emotions. so if you said you got an 80 on a test aand tell her the smile= her being happy for you. that's also how she could just write her texts. wouldent stress over it too much unless you asked her something like "who do you like!" nd she responded with "not telling you ;)"