Ollie":l6mseqb9 said:
Imagine for example that you have drawn a staircase and the spindles are not right, you can just change the dimension or shape of one spindle and they should all change. (the caveat being you do have to "construct" your models correctly using component etc.).
Er, Sketchup does let you do exactly this, very easily indeed.
You can build up components, made from many objects nested "inside" the component (or even components within components, many levels deep), and clone those - any later change to any part of the complex object is reflected in all its clones. You can also take one of the clones and make it unique, so it is unaffected by changes to the rest.
What it doesn't easily do is move everything else to accommodate changes you have made. So you can't easily stick two objects together in a single place/area and have them stay stuck that way no matter what else you do to one of them.
In the case of your staircase, it is very easy to make the spindles as a set, so if the length of one changes the others do, too. But you'd have to move the bannister rail by hand afterwards if you needed to.
Sometimes it's a bit annoying, but it can be excellently quick:
I recently needed to write a safety instruction manual for the kickboard system I'd made for a refurbished tower scaffold. There are lots of machine screws, washers and brackets. I pretty much only needed to draw out one bracket with its bolts and then copy+position the sub-assembly six times to get the quantity I needed. Similarly with the corner pieces and their fixings, etc. That done, I could combine the components in functional sets, which could be hidden or included in images to illustrate the instructions ("Step one, fix the end board..." and so on).
For example, this image shows one of the brackets with its bolts. The sides and other brackets are in the model, but "hidden" to clarify this bit of the task:
And here's the "cloned" brackets all visible: