Backdating a policy means that you can change your policy issue date from the current/present date. The simplest advantage it reflects is on your premium amount. How? While issuing the policy, insurer considers the nearest age of policyholder. Imagine Mr. A is 27 and 9 months old when he is buys the policy. The insurer will consider his age as 28 years old while issuing the policy. But if Mr. A decides to backdate the policy by 4 months, he will be considered as 27 years old.
This will change your premium amount because now you will be paying as a 27 year old. Though the benefits will remain the same.
Effects on maturity:
If Mr. A buys a policy with Plan Term of 20 years on Feb 2019. He can backdate it to May 2018 and his policy will mature at May 2038 instead of Feb 2039.
Note: You can Backdate your policy within a financial year and not more.