Think of it this way: you know what your paper will be about, you have a thesis statement, and you have facts gathered to support your point (the thesis). The body can be written any way you prefer while drafting, shaped up in the editing stage, and wedged in between the already completed introduction and closing you did beforehand. The body will merely have the facts and everything supporting the thesis statement in your introduction, anyway so by taking out the more difficult parts first it leaves you time to tackle structuring the entire essay and as well as establishing a good flow. Handling the flow of your essay is very important to make sure it doesn’t come off as rushed or too sluggish and crawling. So manage your time in everything. You can do the essay the conventional way from start to finish in proper order, just make sure you have the time to do so.