I think that dictation is actually a pretty cool thing. At its best, it combines two people into one, which splits the task of composing/writing into smaller and more manageable tasks.
When you give dictation, you are working purely in your mind. The thoughts you have swim around. The good ones come out of your mouth. They then appear on a page/screen. When you give dictation, you do not have to worry about hitting the keys or correcting errors or formatting as you go.
When you take dictation, you become an intelligent machine. You are able to take in not only words, but pauses and stresses and all other sorts of audio cues and turning it into text. You use free time between thoughts to correct errors and format upon document completion. You are still using your mind, but you are using it in a much different capacity, simply creating words without worrying about creating ideas.
I have been on both sides and actually enjoy them both. If you haven't done it before, give it a shot. One generally does not have much need for dictation, but it may be a fun activity to do with other writers. You will definitely learn how to type faster, speak slower and clearer, and much better understand the connection between spoken words and written words.