I have heard of it. I just don't think that makes any rational sense. Usually when you see three for one coming up, it is purely serendipitous, if I can put it that way. For example, things happen in the jail that cause immeasurable difficulties when a person is awaiting trial that were unknown at the time the trial date was set.
As a practical matter, I really don't see, if I'm looking at a three-year minimum or four years on a gun charge, that I'm going to stay in for two years. Quite frankly, if you go to a federal institution as a young first offender on a four-year sentence, you will be moved into a halfway house in all likelihood by the end of the first third of your sentence. You will have much less restriction than in the Don.