Slang is considered to be informal language that falls in and out of usage quickly with the changing tastes of a culture. In the 1980s, "clutch" was a slang term for "cool" "necessary" or "vital." You may have noticed that that is no longer the case. Slang is subject to such rapid change, and it is used by such selective groups, that it is difficult for slang to effectively express a message. Slang also obscures the meaning of a term or phrase, much like a euphemism.
The use of certain slang terms---those used almost exclusively by a particular group---identifies a person as belonging to that group. With such a small window of usage, slang should be avoided in most writing. Unless the slang is mentioned in the topic you are writing about or you believe that the audience will be better persuaded through sparse use of slang, it is best to leave it out of your academic writing.
Here are some examples of slang:
haven't seen ya in a grip---I haven't seen you in a while
lit up---to shoot someone