Why I-section beam is preferred for heavy loading?

Cross sectional shape I, giving many benefits. It is very good for giving stiffness(less deformation on loading) and to withstand higher bending moments(as a result of heavy loading) on comparison with other cross-sectional shapes of same area. Also, it is very easy to manufacture.

It will have more moment of inertia due to the distance of the flange from the centroidal axis and it have zeron eccentricity about one axis and the centrer of gravity lies inside the web.