The beauty of Seamly2D is that you can make one basic pattern which you can use as the base for other patterns. You will need to save your basic pattern under a different name when you load it to start getting creative for each new design. This saves you the trouble of creating the basic blocks over and over again.
Each person or pattern making system uses a certain set of measurement areas that they use in their pattern making, so it stands to reason that these measurement are used in making the base pattern, so for each person, you can create a measurement file of the same measurement areas and you can resize the pattern by simply changing the measurement file.
There are some areas that may not work so well, that will need some careful thought while making your basic pattern and any additions/changes to it later - the main one is the curves. If the difference in size between the different measurement files is quite big, then these may not curve so nicely. To overcome this, one uses formulas to create the angles and length of the curve handles to make sure that the transition between sizes is consistent.
This sounds very complicated, but with a little practice, it becomes 2nd nature
Like @Scholli, I do all of my drafting using a multisize measurement file so that I can change the sizes while I’m busy and check that the curves work perfectly at each curve. However, once my pattern is made, I often load an individual’s measurement file to export the pattern for printing.