TO CALCULATE TORQUE ABT THE COM has an advantage,

In that case torque due to mg ( wt )  don't contribute.

But torque can be calculated abt any point.

I m not sure hcv told to calculate torque abt ony COM. In fact there r many solved and unsolved examples in hcv where torque was calculated abt a point which is not COM.

For example, hcv , vol I , pg 185, solved example 8----torque was calculated abt a point which is not COM.