This is an important deficiency because it is key to share the design in the most accessible formats with. However, OpenSCAD lacks the ability to export to standard parametric formats thus, the parametric dimensional information of the model is lost.
As wmayer said this is something you usually do at the end of design process if needed but in given task if you can get the same result with refine shape tool from OpenSCAD Workbench then any change should be reflected on refined shape object too. OpenSCAD is the most widely used scripting tool for parametric modeling of open source labware. If i need to change something i just delete that refined shape object and do the changes and create another refined shape object at the end again. I usually use refine shape tool from Part Workbench because it's quite reliable and this "simple objects or solids" are easy to manipulate in FreeCAD. 3 example of unions of 2 objects are shown below: cylinder(r5, h20, centertrue) sphere(r7). Union is what OpenSCAD does by default if you construct multiple objects, it adds the objects such that they build up a more complex object. One tool creates "simple object with cleaned faces (and probably converts the selection to solid if not solid)" as standalone and another tries to do the same but not sacrificing parametric nature. There are 3 primary operations in OpenSCAD, union, difference and intersection.