Standard sofas are built to a standard person who does not exist. Seat heights across the industry cluster within a couple of inches of each other, arrived at by averaging, and that average suits some people very well and others not at all. Anyone tall enough to find their knees higher than their hips on most sofas, or short enough that their feet swing, has met the problem.
It is easy to fix at the point of making and impossible to fix afterwards. Cushion firmness can be adjusted later; seat height cannot, because it is built into the frame.
So our master Indian artisans ask about it before cutting timber. The questions are simple - who sits here most, do they want to sink or sit upright, is anyone finding it hard to get out of their current sofa - and the answers set three numbers: seat height, seat depth and the angle of the back. Everything decorative about a sofa is a matter of taste. Those three numbers are the difference between a piece people use and one they walk past.