The exclusionary rule is one of several remedies available if the police violate the 4th amendment. The rule requires exclusion of the evidence if the 4th amendment is violated. Other remedies include criminal prosecutions of officers, civil suits, and administrative consequences, departmental discipline, etc. Proponents of the exclusionary rule suggest that it deters police misconduct and furthers American values of not basing convictions on tainted evidence. The rule plays a major role in the investigation and trial of any case involving a police search of individuals or property and seizure of tangible evidence.
The exclusionary rule is a way by which the courts try to stop the executive branch from taking over the powers residing with the judiciary.
According to the fourth amendment, the constitution protects citizens from an illegal search of their premises by policemen. It can only be done if the express permission of the court in the form of a search warrant is available.
To make the fourth amendment enforceable and restrict any acts of deviation by members of the police force, the courts do not allow the use of any evidence that has been recovered during a search performed without a search warrant.
Such evidence is to be excluded from use during the trail. This makes it futile for the police to conduct illegal searches as even if they recover incriminating evidence, it would serve no purpose.