Robert wrote:Is it just a matter of looking for things that don't join/work quite right and trying again but bigger or is there a list of actions that will cause problems at 'small' scale and should always be enlarged?
The issue at small sizes is that holes get left because faces don't get made. If an edge is less than about 0.001 in. SketchUp's tolerance settings cause it to consider the endpoints as one. The funny thing is although SU won't create a face with very short edges, the face can exist if it is made at a larger size.If you have a reason to expect you'll be creating short line segments and might run into the holes issue, scaling up helps you avoid the problem.
You can certainly scale up and scale back down again but you'll want to make sure you use the same scale handle for both directions. Otherwise the thing you're scaling can wind up at a great distance from the origin and potentially the rest of the model. I prefer to leverage components for this kind of thing because whatever I do to the larger copy will be done to the original one. There is no need to scale back down and the original stays exactly where I left it. Some folks prefer to use groups rather than components and for them, the method I use isn't an option.
Here's a video that shows what happens if you are creating the tiny faces and don't take the preemptive step of scaling up.