The essence of sam chien is that it is also a "qi kong" (internal strength) exercise. Breathing and control mild tension movement will help develop proper control and focusing of energy and stimulate internal organs.
Many first time ngo cho kun students when introduce to sam chien have diffulty understanding its concept becuase majority of students are expecting more of a direct approach in self defense.
What they don't understand is that, just like building a house it has to start with architectural drawings first, then designing and planning the structural, electrical, mechanical, plumbing, interiors, exteriors and the finishing touches to have a strong livable and bueatiful house that will last for years. In short, long term effect.
That is what sam chien is, developing the foundation, strengthening the internal organs and developing external power, structure, muscle alignment, coordination, concentration, balance and focusing and vitality.
Without a strong sam chien it will be difficult to execute a fighting technique.
Knowing a technique will be useless if one can not apply that technique properly and effectively.