Leeds needed, and still do need, money.
The quickest and easiest way of getting some was selling players, but even the players they sell is controlled by the position they're in.
Only players who have been at Leeds since they were young - Alan Smith, Paul Robinson, Jonathan Milner - will earn the club lots of money.
That's because Leeds would get the whole transfer fee from those sales.
Other players were bought with borrowed money, and in some cases - like Mark Viduka - Leeds don't even own all of the player.
So they would only get a part of any transfer fee, with the rest going to the people who own the other part of the player.
But selling would still help the club, because players like Viduka earn thousands of pounds every week, and if they didn't have to pay them, they'd save cash.