Please note the difference between "useful" and "essential"
A saw this size is somewhat useful up to say, 2". Make a notch, break it.
A saw is very good for precise cuts.
I consider the saws at leatherman multitools very useful. I have very limited experience with SAK saws. They look the same, perhaps a tad smaller, but they may not be the same quality as LM saws. If I don't have a reliable fixed blade knife I would much rather saw halfway through and break it than risking my folder batoning a notch. If all I had was a SAK - I would very much want that SAK to have a saw.
Another way of putting this: There is more than one way to skin a cat.