There's the ~250 or so that they had to turn off permanently because they couldn't get warrants for them, presumably because they could not show probable cause.
The purpose was to require and remind the FBI that they too have to follow the law of the land.
They should have had to get a warrant before they put any tracking device anywhere (and I'm willing to bet they knew that) and they should have been smacked down for every instance where they didn't.
