The Reason for Different Anatomical Body Planes
Most of our human movements are sagittal (forwards and backwards, and up and down), e.g. walking, running and sitting. So when a personal trainer is designing a programme of conditioning, it's important to incorporate other anatomical body planes in the exercises. It should also combine them i.e. a sagittal with a transverse or any combination.
Training will gain benefits if you also include frontal and transverse plane or combine them.