The outlines close to the building are lined up with features of it - doors, window openings, edges. These lines extended out into the garden link the proportions of the garden with those of the architecture of the house in a very satisfying way, felt rather than seen I would suggest by those who use the garden or visit it. The more organic shapes created by the curved lines soften the boundaries and, especially if the garden borders open counvtryside, makes a visual and seamless link with that, merging with the 'borrowed landscape'. Good garden design is a subtle art.
I love the way this integrates the garden with the house aand I love drawing out the plans on the ground. I rarely get to draw on such a big scale!
John Brookes' Garden Design Book chapter 2 Choosing and Using a Grid explains this concept particularly well
Next, the roof..