Yes, we do. If anyone ever wants to know how somebody died, I can use my magic for that.
Bucket capacity is how many spells someone can cast in a day and how powerful those spells will be. If you use up all your magic, eating and sleeping restores it. For some people, that bucket might be like the size of a water glass. Others, maybe the size of a normal bucket. And for others still, the size of a bathtub. Or even bigger. It grows with training and experience, but some people just have more than others.