Yep very common practice with set-up routines that folks use:
1) Set relief
2) Cut nut slots (nut slots can be cut completely independent of the action height and can be finally cut too since we take everything else out of the equation by fretting and holding between the 2nd and third). By eliminating one of the set-up variables, the nut slots the remaining variables can be addressed sequentially.
3) Measure action at the 12th
4) determine desired action (there are specs for generic action, Martin specs and others) and player technique can and should have a say here too. I'll add that string gauges also impact what successful..... action measurements are achievable.
5) Whatever needs to happen at the 12th from our measurements is doubled at the saddles since the 12th is roughly half the scale length.
6) Mill or adjust saddle(s)
7) Observe and remeasure (one of the reasons that the doubling is not always exactly what we want is reducing the height of the saddle also reduces the torque on the saddle, bridge and consequentially the top pull-up and this slightly skews the results one way or another.
8) Bill the customer and get the money....
Easy peezy
Many Luthiers arrive at this on their own. It's also a method that's taught and we teach it in our classes.
Even though the results are not always exactly the function of the doubling it's so very close that it's usually just about right. For electrics with "set flat" trems or hard tail pieces it is closer to exact than it is with acoustics.
One other variable because the strings pull differently at different action heights is the relief. Lowering action can reduce string pull, seemingly.... on the headstock because we are also changing the angle of the pull by lowering the saddles. As such I always recheck relief after dropping saddle height and tweak as necessary.
Related discussions include Martin specs for setting action, how various string manufacturers may intonate differently for the same gauge strings, player technique and the Robin Hoods of the world who think they are shooting a bow and arrow and impact on string lash of string gauge which can be surprising. Understanding string inertia is a good thing to do.....
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