Steak cooks relatively quickly. You are not going to get much rendering. (Maybe you are not using the term correctly? Rendering is slowing cooking so that most of the fat liquefies...generally not what you are after when cooking a steak). So, it depends on your personal preference of how much fat you like on your grilled steak (some of this also depends on the steak quality and fat content). As @Joe points out, trimming some or most fat before cooking is a good option. Searing the edges and sides on the grill or flat top, is really just for coloring, light crisping, or charring, rather than for rendering. In a steak preparation, one is either going to eat that fat or trim it off while eating, depending on your preference. On the other hand, for example, when cooking duck breast, one generally wants the fat between the skin and meat to render out.