The putative justification for the use of the filibuster in the U.S. Senate is to protect the rights of the legislative minority and to ensure that legislative proposals, especially critical or controversial ones, receive sufficient scrutiny before they are adopted—or rejected if the filibuster is sustained and able to withstand a cloture vote (at least 60 votes, three-fifths of the Senate membership). That is the theory.
But, the filibuster also functions in more nefarious ways, such as Strom Thurmond’s unsuccessful, but record-length filibuster against a civil rights bill.