Rekordbox Dj Waveforms

The smallest you can get them is to go to the View menu and select the Browse view. This minimizes the decks, but they are not completely gone.

Also you can undock the Collection part of the screen and put that maximized on top if it still takes to much of your space. The button for this is a tiny little button in the lower right corner, looks a folder icon with a little + in the right top of it.