>>But how do you decide on how to trim just any model? <<

Thats like asking how do you decide to build a model. It depends on the model and output wanted.


>>I've been poly modeling since 1993 ;)<<

I was never really into poly modelling back then. I did try 3d studio and used truespace for a while when it came out, but I was modelling in CAD at work, so that became an hobby when Rhino was first released in beta.


>>I followed your example......IT doesn't magically do what you did.....<<


If it magically did, then I would not need to add trims.
The circular array was just the start, I added more trim lines to cut up the model. It took me about 30 minutes to add the lines/cut up, so its not very quick, but still quicker than some other methods.