The 11mm end gives you a genuinely wide perspective, useful when working in tight locations or trying to establish a large environment from relatively close to the camera. Moving towards 20mm gives a more controlled wide-angle view, making the lens more versatile than a fixed ultra-wide prime. It's particularly handy for architecture, location work, vehicle interiors and other situations where backing the camera up isn't really an option.

As a cinema lens, the ATX has geared focus and iris rings with a long focus rotation, making it much more practical to use with a follow focus or other cinema accessories than a standard stills zoom. The constant T2.9 aperture also means exposure doesn't change as you zoom through the range, which is useful when shooting a continuous move or reframing during a take.

The lens is PL Mount, which means it natively fits PL cameras such as Arri Alexas or some Blackagic Ursa models, and is also very popular converted to E-Mount  for use with Sony cameras such as the FX6 and FX3. 

The relatively compact size also makes it a useful wide zoom for gimbal and Steadicam setups where a larger cinema zoom would be less practical.