I do shoot without them. But when flying bombers, manning field guns or a certain few fighters; they are better with tracers on. To change from a plane with tracers disabled to one with tracers enabled (or vice-versa), you have to click on clipboard, then click on "options", then click on "preferences", then click on "flight options", then click on "tracers", then click on "back", then click on "hangar" and finally pick your new plane - all before you take off.
You don't have to do anything like that to have different pilot views, gunsights, convergence or weapon loadouts when you switch planes. Get my drift?