There's no need to use white out, and in fact, I would stress that there's not a single reason for using white out at all. It takes up too much time, it can be messy, and even though it's good for its purpose, crossing out works just as well and saves you a lot of time too. We were told that teachers sometimes read what is crossed out and if they feel it is actually beneficial, will consider that in their marking (obviously, if it was of no use to your essay, they would just disregard it as you crossed it out).
In short, don't use white-out. It's a colossal waste of time.