Yes, it is mandatory to appear for GD/PI for MBA admission, as personality assessment is a major factor selection of candidates to management schools. The CAT score is used only for shortlisting of candidates for GD/PI. For the final selection, candidate's perforrmance in the GD/PI round matters the most. Candidates who do not participate in the GD/PI round, are disqualified and their seat is offered to the next candidate.