General rule of thumb is to do a lifesaver to check you're not about to pull into the path of another road user. So for example, if sat at a t-junction turning Left, once you decide its clear to proceed, do a lifesaver over your LEFT shoulder to look for any crazy cyclists etc undertaking you. In this situation, there would be little point doing a right hand lifesaver - what would you see? and if you did see something, what could you do about it other than pull left to get out of its way? Also, if you take too long looking behind you, more traffic might arrive making it dangerous to pull out... EDIT: thats my opinion but do what your instructor tells you that you need to do to pass your test!