If you're accused of a crime, one way you can work to defend yourself is by having evidence suppressed. It can't always be suppressed, but there are some instances in which the court will not allow evidence to be presented to the jury.
The first thing you should know is that if your Fourth Amendment rights were violated through an unlawful search and seizure, the evidence discovered at that time should not be allowed to be presented in court. Typically, you'll know if your rights were violated because police will not have presented a search warrant or followed legal means to enter your home or business.
Here's an example: In a situation where you were at home and suddenly found an officer or group of officers entering without permission to search for drugs, you could claim that the officers had no reasonable suspicion, just cause or other reason to come into your home without a warrant. If the officers can't show that they had to enter for time-sensitive or other specific reasons, then you may be able to have all evidence collected during the search thrown out and kept out of any case against you. In some instances, that might mean that the prosecution has no evidence against you at all.
Interestingly, even if you confessed during an illegal search, your confession can't be used in court. The failure to read you your Miranda rights also invalidates any evidence that has been collected during questioning or an interrogation as well as anything that was said during the arrest in some cases.
Source: FindLaw, "How to Suppress Evidence," accessed Dec. 28, 2016