Distance !! That's the big factor IMHO. You can see off "to the sides" at a much greater distance with SI than with any 2d or DI. It's pretty hard to imagine "seeing" anything outside the 60deg cone of 2d or the 75deg fan sweep of DI ... when compared to the ~90deg fan sweep of SI. Not to mention that with SI you can tell which side of the boat the image is coming from ... something you cannot do with 2d or DI.

... cp