When I started with LF many people told me to always make a spare negative to allow for dust, darkroom errors, etc. And this is what I've done ever since. But lately I've been wondering whether this makes sense for me. I rarely need to use a "B" negative, and as a result have boxes and boxes of them undeveloped. So I'm almost doubling my film costs to manage the risk of an occasional error. This doesn't make sense to me, hence my question here: do you make a spare negative?