To add extra panels of fabric under the crutch and arms, this allows the cut to be snug into these areas without feeling tight or constrictive and avoids having four way joints that are bulky and prone to leaking.
By introducing the flex back system instead of a full "telescopic torso" we just have extra fabric in the area we need it to allow bending over in the suit with out straining at the back of the neck seal. The internal braces work in conjunction with the elasticated crutch strap to the panel in place.
By precisely curving the zip across the front of the body so the end of the zip is between the hip and waist then we can keep the front of the suit flat, the zip staying against the body even when sitting down or bending forward without cockling or folding. This distortion of the zip occurs when the end finishes in the traditional place of the upper thigh. The curve also allows the zip to end on the shoulder and not on upper arm which causes restriction when using the left arm.
The reduction of the internal or potential internal volume makes a great difference to air migration around the suit. The less volume the quicker the flow, so when you need to reduce buoyancy air can be shifted to the dump valve position with only a small alteration of orientation in the water.
We cut the legs as close as we can again reducing the internal volume in this critical area.