That is, you can see all the boats around you which are transmitting an AIS signal.
Depending on where you are, that represents about 10-20% of the boats out there (since most yachts, fishing boats, etc. don't transmit AIS signals) and only a tiny fraction of the things which can hit you and which you can run into (like buoys, pilings, lobster pots, dingies, kayaks, flotsam & jetsum, etc.).
Yeah, AIS is neat and fun, but it's not synoptic....very easy to get lured into the belief that thru AIS you know what's really out there.
For me the biggest advantage of an AIS is to make sure ships can see me. I have used a radar for many years and it is very easy to see a ship but difficult to see a sailboat or a small boat specially with waves. With the AIS we are all clear targets on a Ship's bridge.