I guess it also depends on what openings you play as black. For Caro-Kann or French defense you probably only need to know some good spots for the pieces and some typical plans, but if your reply for 1.e4 is e5 (which seems to be the most popular response among beginners), then you'd better be prepared for King's and Danish gambit, Italian or Two knights defense and so on, because in all of these openings it's easy to get mated in 20 moves while making only seemingly logical moves or get into a situation when you have to find the only defensive moves, while your opponent just throws pieces at you and keep making new threats.