KYC is a one-time exercise while dealing in securities markets. Once KYC is done through a SEBI registered intermediary (Broker, DP, Mutual Fund etc.), you need not undergo the same process again when you approach another intermediary.
Prevent unauthorised transactions in your account — update your mobile numbers / email IDs with your stock brokers and depository participant. Receive transaction alerts directly from the Exchange on your mobile / email at the end of the day.
No need to issue cheques while subscribing to IPO. Just write the bank account number and sign in the application form to authorise your bank to make payment in case of allotment.