This is important. So you will practically always get better results with a better microphone than that supplied in the box. Sometimes you will never get decent results with the in-box mic and your particular sound card, so it may make the difference between success and failure. Proof reading, especially from a computer screen, is a difficult skill. We all tend to read what we want to read, rather than what is actually written there.
Proof reading is particularly difficult for dyslexic people.
Even the best dictation system, after you have spent a long time training it and working with it, will make recognition mistakes. Some people will find some of the mistakes easy to spot, as the wrong word will be quite different. To spot these errors, speech feedback is useful, where the computer reads back to you what it has written. But most of all the text reader window, which highlights each word as it reads it, really helps a dyslexic person by making it much easier to follow the reading and focus on the mistakes. Dictation is a bit like riding a bike, and it can be very useful indeed to have the help of someone who knows the ropes and can guide you through getting everything right at once.