You can also use the same technique to categorize your e-mail in more categories then just spam and not spam, I for example have a category for "commercial", eg

You can also use the same technique to categorize your e-mail in more categories then just spam and not spam, I for example have a category for "commercial", eg. newsletters and offers, kinda like Gmail started with some time ago. But I also have more categories, like a category for each project.