2. Why ideal components?

As I already said, when engineer "evaluates" a new circuit idea in his mind, he is using ideal components. Why? Because it is much easier than dealing with real components. Although human's brain is quite powerful, it is more "optimized" for solving problems other than circuit simulation.

However, even with a computer capable to do real simulation, using ideal components would be very beneficial at the initial stage of a project. Why?

First, even if calculations are done by computer, an analysis of the simulation results will be performed by a human. With simple ideal components it would be much easier to understand how schematic is supposed to work, how parts of the schematics and individual components interact with each other, and how each component (or component's parameter) affects circuit functionality.

Second, even NL is not a perfect tool: all simulation algorithms and methods have some limitations and may introduce some inevitable errors while converting "real world" into numbers, manipulating those numbers, and finally presenting results. With real components, separating math "artifacts" from actual schematic problem could be a very difficult task. With ideal components, any "strange", non-expected schematic behavior could be analyzed better.

Third: although new Spice simulators are extremely fast, using simple components could definitely accelerate simulation a lot (of course, if simulator can handle ideal components properly). Engineer is designing a new schematic still in his head, using simulator as an external "add-on tool" to evaluate ideas. For productive work, simulator should be literally as fast as human's brain is: providing response as fast as possible and not to be a "bottleneck" in the design process.

Fourth:.. we'll find out more reasons later, while discussing what NL5 is.