What are the meaning of and the biblical basis for the practice of pleading the blood of Jesus in prayer?

I've heard people say this phrase in prayer many times. A simple [Google search](https://www.google.com/search?q=%22plead+the+blood+of+jesus%22&oq=%22plead+the+blood+of+jesus%22) for the exact phrase *"plead the blood of Jesus"* confirms that this is the case, returning about 280,000 hits (as of April 2021). My superficial understanding is that people usually plead the blood of Jesus expecting some kind of special spiritual protection against the dark forces, maybe it has something to do with spiritual warfare, I'm not sure. Questions: 1. What do Christians mean when they plead the blood of Jesus in prayer? Is there a canonical definition of the phrase? What do they expect will happen when they say it? 2. What is the biblical basis? Are there scriptural examples in which an apostle or a disciple pleaded the blood of Jesus for protection or any other purpose?