Redundancy vs. Dependency
Dave Shea describes the two different ways of dealing with CSS cascading: Redundancy vs. Dependency.
Most of the time I end up doing what Dave describes: start off with dependencies, and as a project nears the end, more and more redundancies end up in the CSS. Adding redundant CSS can really annoy the logical and structured part of me, but sometimes it does make things easier to understand. Like Dave says, that can be very important when other people will edit the CSS.