After the Commonwealth (or State) rests in your criminal case you will have a chance to put on a defense by providing evidence and testimony. One such evidence is your direct testimony, i.e, you taking the stand. But should you? Theoretically, the trier of fact (a judge or a jury) cannot hold it against you if you don’t because the 5th Amendment of the US Constitution prevents self incrimination (“no person may be compelled to testify against himself”). Whether that actually happens in reality is hard to tell since in the back of everyone’s mind is “if he has nothing to hide why doesn’t he take the stand?” Even so, more often than not defendants doesn’t take the stand in a criminal trial because of the risks involved.
What are the risks? Well, people get nervous taking the stand and are not as good on the stand as they think that they will be. Even if he the defendant didn’t make a statement he could be caught in a lie, inconsistency, exaggeration, or a story that doesn’t make sense. And that, coupled with previous evidence, might seal the conviction for the Commonwealth. Obviously if the Commonwealth did not have enough for a conviction without the faulty testimony — this could be a disaster. However, sometimes in a he said, she said type of case (rape, assaults) the defendant doesn’t have much choice because otherwise the trier of facts only hears one side of the story. It is not always clear whether the defendant should take the stand but you should generally listen to your criminal defense attorney who has the experience to make this judgement call.