Question

Why pendulum is preferred sperical in shape?

Answer 1

Answer: A pendulum is preferred spherical in shape because:

1 - Due to its asymmetric nature, air resistance might more likely result in an undesirable twisting oscillation or perpendicular swing component.

2 - A spherical bob, save for the small non-ideality of air resistance   and cord mass, will act as an ideal point-mass pendulum, of length equal to the cord length plus the sphere radius.