When you need to shave, but decide not to because of an important event coming up. Saving your shave is done to eliminate any irritation you would receive from shaving too often.
Guy1: Dude you haven't shaved for like a week, you need to get on that.
Guy2: Yeah I know, I'm about to.
Guy1: On second thought, you should save your shave for when your girlfriend comes this weekend!
Guy2: Oh good idea, I wouldn't want razor burn while she's here