The premium for a term policy is guaranteed for a certain number of years. If you cancel the policy prior to the end of that term you will have paid slightly more for the coverage than was necessary. Few term policies have any cash value so there isn’t anything to offset the cost of having carried the policy. However, if the policy has done its job and is not needed any longer it is not necessary to keep it.
Another way to look at it is Term Insurance is like Renting an Apartment. It’s typically cheaper than paying house payments as a homeowner and if you move out of the apartment (cancel the insurance) then you get nothing back. It was just a place to live for a Term Period. On the upside – rent can go up every renewal whereas if you buy a 10yr, 20yr or 30 yr term – the rates are level for that term period.