Here's why:
* Formal speech aims for clarity, precision, and professionalism. Slang is often informal, can be regional, and might not be understood by everyone, making it inappropriate for formal situations.
* Casual speech allows for more relaxed language, including slang, idioms, and colloquialisms. It's used in everyday conversations with friends and family, where the goal is to communicate easily and naturally.
Here's an example:
Formal: "I am currently experiencing a significant amount of difficulty with this task."
Casual: "This thing is totally messing me up."
Using slang in a formal setting could be jarring and undermine the tone you're trying to achieve. In casual settings, slang adds authenticity and realism to the dialogue, making it sound more natural and relatable.