You are instructed to cool the recrystallization flask to room temperature and then to 0 °C ""to maximize the recovery of desired material"" ... how does this maximize the recovery?

So that some of the sample doesn't dissolve

Explanation:

This happens because of the chemical properties of the material, which is that, when it's at a certain temperature that is not too cold and then it's cooled at a very drastic rate, the material will actually grow on size and this prevents the material form dissolving.