Here's the situation: Final turn of the game, 3 players are placed in the castle, orange, blue, and black (me). orange gives 2 batches, blue 3. I have 4 batched, but now there are only 2 open spaces left. I was planning on building 4 specifically for the favor.
If orange and black give 2 batches each, and blue gives 3, then blue gets the favor - even if you would have had enough resources to build more.