STEP files are like compiled binaries. Fine for distribution if you don't want to make changes to the file. But for a parametric CAD package like Solidworks or

STEP files are like compiled binaries. Fine for distribution if you don't want to make changes to the file. But for a parametric CAD package like Solidworks or Onshape, much more information is saved. A parametric CAD file stores each step done to the part in order. This allows you to go back in time, change one feature, and re-apply the subsequent changes to the updated file. That's like source code to the part.