First of this isn't a question, but here we go! Figurative is GREAT for academic writing. It can convey points and make things easier to understand. It also makes the passage more lively, and less boring (No one likes a boring paper).
Though colloquial isn't good for essays, if it is in dialogue it is okay. For instance, it shows the culture of the person, and makes for some interesting reading! "If dats aright' fer ye!"