There are times in the life of any homeschool parent when they encounter subjects they can't adequtely teach their kids. While books will always be available to fill gaps, sometimes the best option is to simply find someone else to teach what you can't. For those situations, there are curriculum DVDs.
Advantage #1: Instead of wasting unnecessary time reading and reiterating information, you can get rid of the middle-man element and simply set your kids in front of the TV or computer. If this was a babysitting method, we'd be opposed to it, but in the case of school learning, it's a positively brilliant option.
Advantage #2: Kids who don't do well simply reading books will find this kind of instruction more helpful. Audio/visual lectures, especially if supplemented with entertaining elements, are much more likely to impress the relevant information on kids' minds than books, and will likely do so in such a way that they'll retain what they've learned.
Some DVDs present information to parents instead of students; the benefit is that, by watching someone else present the material, parents will have a better idea how to pass it on to their children. In programs like this, the lecturer typically imparts much more to teachers than they're responsible for passing on, thus giving them enough background information to help field questions.
While the future of education is probably on the Internet rather than discs, the courses offered here are great examples of how modern technology can be used to excellent purpose. We don't encourage anyone to get rid of their books, but we also don't want you to be so controlled by them that you can't take advantage of excellent resources like these.