Well, if waterjet works anything like laser (we had a big one at work), then you just barely need to clamp the work. Gravity does its part, and I imagine the cutting force would be aligned with gravity, pushing the work into the table. So the setup really is simple and easy, and you can cut parts off the sheet and let them just drop.
By contrast, milling tools will try to push the work in all directions depending on what kind of cuts you're taking at the moment. They will also try to pull the work (and if the work is loose, you can easily shatter tools). Of course the countering forces affect the tool and through it the rest of the machine, which needs to be rigid enough to take it. The workpiece and the part that will fall off must be clamped accordingly, and then you run into the issue of tool paths that would cross over your clamps, so you'll need the operator to re-clamp things in the middle of the job. And there are clearance issues when you try to operate small tools near clamps. It's definitely harder to set up, and more involving than a laser that just needs a path and then cuts it all up for you after you press play.
I don't know what exactly the state of the art of hobbyist scale machine tooling is right now, but I would be surprised if high speed (=> suitable for small tools and low forces) CNC mills were commonly available. Most hobbyist machines I've seen are neither rigid nor CNC, so you won't be easily cutting smooth & complicated shapes with them.
"Well, if waterjet works anything like laser (we had a big one at work), then you just barely need to clamp the work. Gravity does its part, and I imagine the cutting force would be aligned with gravity, pushing the work into the table. So the setup really is simple and easy, and you can cut parts off the sheet and let them just drop.
"
Go hit part of something not flat to within a few microns with 75k psi of water and see if it vibrates :)
Also, unless your nozzle alignment is perfectly vertical, there is some sideways motion imparted.
(IE you are kinda right, but you still gotta do something)
Particularly for small pieces, it can be a pain in the ass. On the plus side, yeah, light clamping with c-clamps/etc works most of the time.
By contrast, milling tools will try to push the work in all directions depending on what kind of cuts you're taking at the moment. They will also try to pull the work (and if the work is loose, you can easily shatter tools). Of course the countering forces affect the tool and through it the rest of the machine, which needs to be rigid enough to take it. The workpiece and the part that will fall off must be clamped accordingly, and then you run into the issue of tool paths that would cross over your clamps, so you'll need the operator to re-clamp things in the middle of the job. And there are clearance issues when you try to operate small tools near clamps. It's definitely harder to set up, and more involving than a laser that just needs a path and then cuts it all up for you after you press play.
I don't know what exactly the state of the art of hobbyist scale machine tooling is right now, but I would be surprised if high speed (=> suitable for small tools and low forces) CNC mills were commonly available. Most hobbyist machines I've seen are neither rigid nor CNC, so you won't be easily cutting smooth & complicated shapes with them.