The golf instructor Harvey Penick often told his students the secret to good golf was to think on the practice range and concentrate on the golf course. To think on the golf course is to court disaster because thinking gets in the way of doing what should be routine. I think this also holds true when photographing. Having complete confidence in your ability to handle the camera and its controls reflexively leaves a whole lot more mental energy available for the creative part of photography.
For the many years I took a view camera on the photo safari, part of my pre-trip preparation was to get out the view camera and practice setting up the tripod, unfolding the camera, attaching the lensboard, focusing and setting the shutter. It was a necessary activity to insure that I could “get the shot” when faced with rapidly changing light.
All these years later I still practice before I head out for any serious photographic expedition. Even if it's out in the backyard, down the street or across the country. Physical mastery of the equipment you use is a necessary part of being an artist because when it comes time to create spontaneously you need to have your equipment function without your thinking.