Once upon a time, memory was far more expensive than today and was only available in smaller quantities. When a system has 128MB of RAM, you want every bit of that to be available for work. It was important to have a kernel as small as possible. Today, when even a laptop has 2GB RAM, kernel size is almost irrelevant. Stripping unnecessary drivers out of a kernel to make it smaller might not be vital—but it isn't an actively dumb thing to do; it will teach you how to build a kernel, so that when the need appears you won't have to learn something new. So, we're going to use kernel trimming as a learning exercise, but don't consider it vital or even necessary.
Remove an entry from the kernel configuration by commenting it out.