Question

what is point group theory

Answer 1

any of the 32 sets of symmetry operations which can be used to characterize three-dimensional lattices and are the basis of the system of crystal classes.

Answer 2

Symmetry is very important in chemistry researches and group theory is the tool that is used to determine symmetry. Usually, it is not only the symmetry of molecule but also the symmetries of some local atoms, molecular orbitals, rotations and vibrations of bonds, etc. that are important.