I use slang mostly with my friends and family, while at home or in town. I also use it in school, but rarely. I use slang in common situations, while commenting on something, joking, talking about something that is niđe veze ( nigdje veze-correct).
Why do I use it? I use it because, sometimes it is easier to speak in slang (you don't have to think about right grammatical forms, word order, or vocabulary, you can just use it without any rules). I use it because it can also be funny, interesting, and it can distract one's attention (for example, if you are reading some philosophical article and you are board, and then suddenly you see slang you will probably be surprised, awakened and more interested in reading the rest of the article. I use it because my personal slang "separates", "isolates" me from my company, society and lets my personality be recognizable through something that is unique only to it.
According to the definitions we heard from the BBC's "Learning English" radio programme, Talking About English, episode Part One of "Politics, Language, and Slang", slang is non-standard, very informal language, using non-standard word which has standard word. I agree with these definitions, but I will also add that slang for me represents street language, language of a specific type of music, language of experimenting with the language itself.
Slang comes from people's desire to shorten the words, make them less formal, easier to communicate, not so strict and grammatically correct. It is usually spoken, and it has its tradition, like Cockney for example. Cockney is a traditional slang, a "secret language" used by people which worked in the market for customers not to understand them.
In my opinion using slang can be good, but it can also be unsuitable, e.g. if you're a politician, and you're using slang, people certainly won't take you seriously enough, they will start laughing at you, or even worse, they won't consider you educated enough to perform the function of the politician (represent them, their name, culture, and country in the world).
Also the bad side of slang is that not everyone understands it. If you are using slang while speaking to an older person you could get misunderstood. Most of the older generation doesn't understand slang that younger generations use, e.g. if you say to your grandfather Come, and hang out with us, he will probably think you're hanging on something, a tree, or something similar. Simply he won't understand you. That is why we have to be careful when using slang, we need to be aware that not everyone knows what we are speaking about.
Everyone uses slang: politicians, lawyers, teachers, musicians, actors and actresses, farmers, TV hosts... It's present everywhere, in every profession, and in every part of society. Some use it more, some less depending of their own acquaintance to it, of the social circles in which they move, of the age structure, and their desire to use it. It is widely spread, and it is a popular form of communication that is becoming more frequent every day.