Non-aggregating mode allows the port to run at full line rate, without dropping traffic. You need to use 2 ports on your monitoring device to watch both sides of the network link.
Aggregation mode also creates identical copies of the aggregated data on the tapped network link. This mode allows 2 monitoring tools to be connected.
Live network ports support PoE passthrough. e.g. allowing monitoring of SIP traffic on a phone handset that requires power via PoE