It is not a good idea to ignore torsional irregularity even if the displacements are too small.

Hi Ahmad:

The torsional deformation isn't really important in some buildings, depending of material. In steel building, the torsional effect isn't important, but in concrete building, the torsion can produce the collapse of the building.

Anyway, you can resolve this dilemma with the rigidity center. If you can coincide this center respect to mass center, the effect of the torsion dramatically reduces.

Greetings.