Hi Prakash, Signing POA is not compulsory. POA authorization is required to the brokers to debit the shares from your account whenever you sell the shares or when you participate in tender offers like Buyback, OFS(Offer For Sale), Takeover, Delisting etc.
In case if you wish to sell the shares without providing POA then you can do so using E-DIS facility (Know more: https://tradesmartonline.in/help/back-office/can-i-sell-shares-without-physical-power-of-attorney-poa/). E-DIS is nothing but through the TPIN process as you have mentioned. However, we recommend you to provide the POA hard copy for the smooth functioning of your trading activity and to avoid any inconvenience.
In case if you wish to participate in tender offers, you are required to provide the signed hard copy to the brokers. Because SEBI has not yet come up with the online facility for tender offers. Know more on tender offer - https://tradesmartonline.in/help/trading/how-to-place-buy-back-request/