It is a default option. It works only while the user’s computer is running and as long as remote NEM infrastructure server (NIS) is connected. Advantages are that no setup is required. The user just has to click on “Start local harvesting”. Disadvantages are that it is more expensive since the computer must be running.
It requires a connection to remote NIS. Delegated harvesting must be activated explicitly. The activation of delegated harvesting has to be done only once and it costs 6 XEM. After 360 confirmations (up to 6 hours) the activation is completed. The user can check the harvesting panel which indicates whether harvesting is ACTIVE or INACTIVE.
Advantages are that harvesting is permanent even if the computer is switched off (remote NIS harvests on user’s behalf). So it is more cost effective. However there is one risky point.
For delegated harvesting remote NIS needs to have the user’s private keys so the keys are sent via network. Key transfer is highly secured. Please carefully read the documentation to activate delegated harvesting in a secure way.