In practice, this means that a senator may privately provide notice to their party leadership of intent to object to a motion.
The leadership can more easily schedule business if they know in advance which unanimous consent requests are likely to receive objection.
The ability to place a hold would allow that senator an opportunity to study the legislation and to reflect on its implications before moving forward with further debate and voting.
[4] In August 2006, the Federal Funding Accountability and Transparency Act of 2006 was put on secret hold.
During the 110th Congress, Senator Tom Coburn put holds on a significant number of bills, raising the ire of the leadership and forcing them to package many of the bills with holds into one Omnibus Act (the so-called "Tomnibus") at the beginning of the 111th Congress.
During the 118th Congress, Senator Tommy Tuberville put holds on all military promotions and nominees because he opposed the Department of Defense policy to reimburse travel expenses for military personnel who have to leave their states to get abortions or other reproductive care.
[9] Secretary of Defense Lloyd Austin has criticized him for the risks posed to national security by leaving hundreds of military posts vacant.
[15] Enacted on September 14, 2007, the Honest Leadership and Open Government Act of 2007 amended the Senate rules to require public notice of holds within 6 session days.