I don't see blender as a dimensional accurate parametric CAD tool although it may be able to do that.

In FreeCAD and others like Fusion 360 you create sketches on planes with dimensions that can be variables. You then extrude, make more sketches based on previous features etc. This allows you at a later time to change the value of a dimension and it propagates through the entire part.

When it comes to 3d printing I use this a lot of things like lids which need to snap on. There is a certain amount of spacing between the lid of the box which may need to be adjusted to get the right amount of "snap". With parametric modeling I can just go and adjust the variable of my gap to be a bit smaller or larger and it will adjust all places where this applies.