AIS is overall fantastic, just for the fact that it gets rid of endless “calling the vessel in position xx, cse xx, spd xx” calls. It is nice to know that you can usually call someone by name on the radio. It is a useful backup to what the ARPA is indicating in that I like it when they both tell me similar info on a contact.
On the flip side, there can be a lot of variation in the quality of data that is being broadcasted over AIS, and you have to take everything with a grain of salt. We have all seen that ship icon on the ECDIS cruising along a course of 090 with their heading stuck at 000. Or the ship clearly at the pier loading cargo, but on the screen a few cables inland.
Some of the data seems pretty needless for most users. Why do I need to know the destination of a vessel while on watch? It can somtimes be useful in predicting where a vessel may be about to turn in a busy area such as leaving a port, but of all the misinformation I have seen, destination seems to be the most common. It’s also a security risk that some may exploit.
AIS is required for most of us now, but it seems that there is little to no enforcement of making sure it is being used properly. Some ships are great about it, some half ass it, and some turn it on and off at will (MSC). I am guessing it will be integrated into the next STCW changes we are all going to have to face as well.