The intent of a fish scaler is to literally scrape the scales off of fish. I have NEVER needed one, and while I can't be 100% certain that I never will, I feel confident in making that assumption. They are there, as far as I can tell, because they are cheap and easy to make, and people look at it and think (it's got a saw!).
I know this because I have watched a number of youtube videos where people either assumed that a fish scaler WAS a saw, or stated directly that they could use the fish scaler as a saw. This is not true. In fact, on some cheap MTs, you can't even use the SAW as a saw (as with SAK knock-offs).
I would almost like to see a video of someone trying to cut a branch with a fish scaler. I'd be all