The fourth amendment protects against an unreasonable search, meaning someone can't search your house or belongings for evidence without having a warrant.
The Fourth Amendment to the United States Constitution is one of the provisions included in the Bill of Rights. The Amendment is about the protection of arbitrary investigations and apprehensions. It was established in response to the controversial writ of assistance (a kind of general order of registration), which played an important role after the United States War of Independence.
If this amendment did not exist, people would not have protection against government actions, as this could stop anyone or search in private property without any warrant or apparent reason. Therefore, this amendment is necessary to guarantee the rights of American citizens.