升級標準代幣的主要用途和目的是什麼？

contract StandardToken is BasicToken, ERC20 {

mapping (address => mapping (address => uint)) public allowed;

uint public constant MAX_UINT = 2**256 - 1;

function transferFrom(address _from, address _to, uint _value) public onlyPayloadSize(3 * 32) {
   uint _allowance = allowed[_from][msg.sender];

   uint fee = (_value.mul(basisPointsRate)).div(10000); //because 10000 Basis Points == 100% percentage terms
   if (fee > maximumFee) {
       fee = maximumFee;
   }
   if (_allowance < MAX_UINT) {
       allowed[_from][msg.sender] = _allowance.sub(_value);
   }
   uint sendAmount = _value.sub(fee);
   balances[_from] = balances[_from].sub(_value);
   balances[_to] = balances[_to].add(sendAmount);
   if (fee > 0) {
       balances[owner] = balances[owner].add(fee);
       emit Transfer(_from, owner, fee);
   }
   emit Transfer(_from, _to, sendAmount);
}

function approve(address _spender, uint _value) public onlyPayloadSize(2 * 32) {


   require(!((_value != 0) && (allowed[msg.sender][_spender] != 0)));

   allowed[msg.sender][_spender] = _value;

   emit Approval(msg.sender, _spender, _value);
}

function allowance(address _owner, address _spender) public constant returns (uint remaining) {
   return allowed[_owner][_spender];
}

}

contract UpgradedStandardToken is StandardToken{

function transferByLegacy(address from, address to, uint value) public;
function transferFromByLegacy(address sender, address from, address spender, uint value) public;

function approveByLegacy(address from, address spender, uint value) public;
}

我認為的主要目的是使契約向後兼容，ERC20同時擁有自己的transfer和transferfrom自定義的業務邏輯。

引用自：https://ethereum.stackexchange.com/questions/64534