What is the usage of pleading not guilty if you are later to be found guilty?

What do u mean by usage?

Especially in Criminal Law, the accused will be examined initially before putting him/her into full fledged trial, for the accusations on him/her, if he/she pleads or accept that they are guilty for the accusations leveled on them, the court will cut short the process as per the criminal procedure followed by the respective countries and proceed with the verdict.

In other case if the accused pleads not guilty, court will proceed with the full fledged trial according the rules and procedure of criminal law of the respective countries in order to ascertain the facts and accusation leveled against the accused. In the process of trial, court finds the accused is guilty, then the court convicts the accused accordingly, otherwise court acquits the accused from the charges leveled against him or her. Thanks