This AOL article explains a number of reasons for using the no-knock warrant. One mentioned is that when this kind of warrant is executed one cannot use Fifth Amendment protections. Also many comments, some informative.
I was trying to figure out how the Fifth Amendment factors into it. I guess the answer is that they are talking about subpoena v. warrant. With a subpoena, you’re asking the subpoenaed party to make a decision as to what is relevant, and in doing so, you are basically making an admission. With a warrant, the officers executing the warrant make that decision.