Answer:
The decisions in Miranda v. Arizona, Gideon v. Wainwright, and Mapp v. Ohio are very important to defendants in criminal proceedings today because they enlarged defendants' rights in criminal trials and investigations.
Thus, Miranda v. Arizona refers to the fact that those accused of a crime must know their rights prior to being questioned by the police, that is, that everything they say can be used against them and that they have the right to consult a lawyer.
For its part, Gideon v. Wainwright guaranteed the defendants the right to have a lawyer, even when they could not afford it on their own financial means. In this way, a defendant is not left legally unprotected for not being able to afford a lawyer, since it is the state that grants him one for free.
Finally, Mapp v. Ohio prohibits the use of illegitimately obtained evidence in criminal proceedings. Thus, non-compliance with the Fourth Amendment (and the consequent search without a warrant) renders the evidence obtained in this way not admissible in court.
