The name NB-IoT simply means narrow-band IoT. It is a newly developed standard to let IoT devices and sensors to operate via carrier networks. The uniqueness of NB-IoT standard is that it just needs just 200kHz of bandwidth for its operations. Hence it supports a large number of endpoint devices with a very lower power requirement which allows it to be used by small sized, less complicated IoT gadgets.
If you have got a potential IoT use case which involves coverage of huge areas, where it might be totally impossible or you know impractical to implement your own radio coverage, Narrow band IoT is a potential life saver for you.
Narrow Band IoT is more power efficient and can deliver great range and throughput at a very low price.