When water freezes it expands. Ice crystals destroy cell walls in your fruit turning them to mush.
By first lowering the temperature on the berries in the fridge before placing them in the freezer, you allow the freezing process to take place much more quickly, minimizing damage. Your berries will remain relatively firm even after they thaw.
Keeping the berries separated on a cookie sheet also makes them easier to pour into a freezer bag for long term storage.
Retrieve by the handful come winter. They're a natural addition to smoothies, in cereal or with a bowl of ice bean!