An undercover guy was in a bar and had a conversation where a guy he knows to be a really bad person tells him to stay out of the subway for the foreseeable future. He leers and says that he's heard something really big is going down. He doesn't know much but what he does know sends a serious chill down the back of the good guy. The undercover guy tries to get more information but can only learn that the guy found out about this while overhearing a cell phone conversation in a bar last Thursday.
He contacts his bosses with the information. The undercover guy is hopeful that the problem can be tracked down because the bar where the cellphone conversation happened probably only had twenty people pass through it on a quiet Thursday night. There would only be a handful of cell calls from the place. That list should be available at the click of a mouse. Finding the cellphone on the other end should be another click. A quick check of the location data for those phones reveals that they have been talking to a phone that came up in another investigation.
Wait! They can't do that. We decided that, instead of "a click of the mouse", they had to fill out a form, get a warrant and wait for those things to be approved. Oh, and they had to know the name and phone number of the guy in the bar before they could get the warrant. Since they don't know that, they don't even apply.
The government defenders are saying that a plot to blow up bombs in the New York subway was foiled a while ago. Imagine how frustrated that undercover guy and his support team would feel as they thought about that overheard conversation. Imagine how annoyed you'd be at your mother's funeral.