Operator vs Approved Account

[ijxy]

What is the purpose of having a designated operator instead of utilising the approve/transferFrom mechanism popularised by ERC20/ERC721 standards?

Are there features that can not be readily implemented using approve/transferFrom/transferFromWithData? If not, then what is the purpose of operators?

[ijxy]

NB: I understand that the concept of operators or controllers has been introduced for forced/mandatory transfers. My question is really why can't this be achieved with the approve/transferFrom mechanism?

For example, one potential way of doing this would be to have transferFrom (or transferFromByPartition or transferFromWithData, etc) implement specific logic when called by issuer (designated address) to bypass the issuer allowance (i.e., enabling forced transfers at the discretion of the issuer).

[pynixwang]

approve must be called with token holder.