Metering on Neutral or Live Line

According to the datasheet, metering can be done on the L line and the N line.
On the L line metering a shunt is connected and metering is done.
On the N line metering, a current transformer is used and this is added when there is a plan to meter the neutral line for anti tampering(L+N metering).
Why was the metering done on the Neutral line ? Is it capture energy consumption in a situtation where customer by passes the life wire ?
What happens when there is a fault on the live wire and current flows from the live to the ground without returning through the neutral?