Whenever I get a multi-tool knife now, I skip over the ones which do not have the saw. I do not understand why you can get one with screw-drivers, hole-punchers, and even corkscrews, that would then not also have a saw.
I have used the tiny saw on my multi-tools, including the Victorinox Swiss type you have, many times. They get through saplings and small branches way better than trying to whittle through it with the knife.
I have whittled through them with knives as well when no saw was on hand. That can be done, but it takes longer, is less efficient, and does not leave as nice an end on the wood.
The appropriate size range is small, yes. Wood too small, you could just snap it off, or small/green you can bend it and make a simple knife cut through the weakened part. Too large, then the saw will not get through.
We need to remember what these multi-tools are for. They are not for fully replacing our larger tools of the same type. They are for quick use to avoid getting the larger tool out (or going to fetch the larger tool), or for emergency use when you do not have any larger tools.
If I either don't have a proper saw or don't want to keep getting it out and re-packing it dozens of times, then I am going to try to void using any tools at all, breaking sticks with my hands or feet. Not even a knife is completely necessary here. If I have a knife, that slightly increases the reasonable size I can process. The tiny multi-tool saw does the same thing again; it slightly increases the size of wood I can process.
If you have tons of wood of the size you can process easily with your hands and a knife, then the tiny saw is not necessary for you. If you have less wood options and would like to slightly increase the size of wood in your "easy to process" range, then the saw does that.
So it's not way super useful, but it's a "Why not?" I would much rather have that saw than a corkscrew or leather hole punch.
That said, if you can find a multi-tool that includes a knife and saw both larger than the normal multi-tool, say double the size, then that would be awesome. The saw would be much more useful. Let us know if you find such a thing. But even if not, the tiny saws on our conventional multi-tools are still better than no saw.