As far as things being cleared NRN, it could be, like in the case of a man sitting in front of his house, that it is just suspicious in nature and while it warrants no report being taken, the incident can be kept on file for future issues with that residence/person. The person could be someone who suffers some sort of mental problem. If there isn't a report taken then whatever info the officer had (street address, license plate, DL#, persons name) will be lost by the start of the next shift unless he requests it hard copied.
As far as license plates and name readbacks, the vehicle could have been involved in a traffic accident, or like i believe scanner freak mentioned the person could have warrants. Beyond that i really can't tell you.... things normally aren't hardcopied for no reason so i would have to assume that there was more going on then what was getting out on the radio. Cell phones are the new wave of police communicating with themselves and with the dispatch center so a lot of times the real interesting stuff never makes the radiowaves.