But why throw hundreds of pounds of equipment at a minor problem (which, incidentally will not work) when a £20 block or hand plane will do the job?
A Dutchman in the edge of a door looks like this:
By its' nature you cannot make them dead to size and guaranteed getting a dead fit, sio we make them slightly oversize (a couple of millimetres) then trim them in. But how do you deal with the little lip which will be left projecting from the face when the main projection has been removed?
If the door is veneer-faced or is a hollow door you just can't run a belt sander on it as it risks going through the surface veneer, soime of which are well under a millimetre thick. Run a random orbit sander on it alone and you'll probably dub over (round off) the edge of the door (and you'll stil risk going through the veneer) whilst a saw with a rail (track) cannot be clamped onto an edge that narrow. Best solution is a cheap block plane and a bit of hand sanding
But there are far more Dutchmen applied to door casings, in the rebates, than doors, because often a door is being replaced whilst the casing is not. In that instance you can't even get a rail saw in to do the main flush cut because therere is no guarantee that the architrave you need to sit the rail on is level, most of the time the architrave isn't wide enough to support the rail (you need about 100 to 120mm to support a guide rail - architraves are often just 50 to 70mm wide) and there is no easy way to secure the rail in place, vertically on the architrave - and that's before you hit the issue that a guide rail is 5mm thick, the architrave is 18mm thick and the hinge leaf is 35 to 38mm or so deep = 61mm whilst most track saws have a maximum depth of 55mm. So your saw can't make a deep enough cut
Again, this is a task for a humble block plane.
Don't get me wrong, I'm all in favour of power tools for a lot of tasks (without them I wouldn't earn a living), and the plunging rail/track saw is one of the better tools to have come to the fore in the last 2 decades (I wouldn't be without mine). It's just that this isn't a task which can be accomplished with one. Sometimes simpler is better