A person who has been charged with a crime is always given the chance to respond to the charges leveled against him. He is expected to give one of three responses. He can say he is guilty, not guilty, or he can give a no contest plea. He can also refuse to give a response, at which a plea of not guilty is automatically entered in his behalf.
A no contest plea means that the person is not denying the charges, but he is also not claiming guilt for the said charges. This is a convenient plea in that it can save time if the person charged must enter a plea for each of the charges. But while the person charged has not entered a guilty plea or contesting the charges against him, a no contest plea is often considered as guilty. If the sentencing for the charge are done immediately then the said plea will not have any kind of weight when the judge gives his sentencing.
A person who wants to be able to defend himself against the charges against him will not use a no contest plea. There are instances when the court is petitioned to change the plea, but this is not always allowed by the court.
But there are also some cases in which the defendant who feels that he cannot win the charges but also want to give the court the perception that he is not guilty will usually be asked to give a no contest plea because this plea will usually go in to a plea bargain.