all I found was that it enhances tamper-detection techniques
A 3P e-meter can still operate, and can measure phase currents, without having the neutral connected.
Let's assume the neutral is not connected to the meter. R, S, and T phases pass through the meter and goes to the end user. Any phase-phase combination usages can be logged by the meter. But if the end user brings a neutral then he/she can use any phase with that neutral illegally and the meter will not be able to measure it correctly.
If the meter measures the neutral current then it can compare it with phase currents and can detect any illegal usage. We know that the neutral current is zero in a perfectly balanced system, so this may not work in perfectly balanced systems; but in practice there's always an imbalance. So, measuring the neutral current can work anyways. And it's the cheapest and the easiest-to-apply way for tamper-detection.
PS: Here in Turkey, illegal electricity usages are quite high in south-eastern region. So TEDAŞ (Turkish Electricity Distribution Corp) have been renewing existing 3P e-meters with ones having neutral current measurement.