Why does OpenZeppelin implement increaseAllowance and decreaseAllowance functions differently in their ERC20 contract?

Question

This is copied from their ERC20 contract from github (https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/ERC20.sol):

function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
    _approve(_msgSender(), spender, _allowances[_msgSender()] + addedValue);
    return true;
}

function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
    uint256 currentAllowance = _allowances[_msgSender()][spender];
    require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
    unchecked {
        _approve(_msgSender(), spender, currentAllowance - subtractedValue);
    }
return true;
}

Why would they not be implemented the same way?

Answer 1

In PR #2669 where those changes were made they mention Issue #2665. In that issue a comment by vladyan18 points that using unchecked reduces gas usage at deployment by 1723.