Yes, especially if running train(s) on the mainline while switching cars, tearing down and building up trains in the yard is in your plans, you want to have as little interference between those two sets of activities as practical. Using the ends (or middles) of mainline sidings to access industries, yards, service tracks, roundhouse, etc. would work well to isolate those activities while also providing ease of transferring trains to/from the mainline. The Styrofoam ramps from Woodland Scenics are excellent for easily providing a smooth, uniform slope for the trackbed, regardless of whether the tracks are straight or curved. But there are also other ways to accomplish that, depending on your skills, and what your layout base will be (foam, cardboard/plaster-cloth with splines, cookie-cutter plywood/masonite, etc.) But if you have the skills to scratch-build bridges, etc., you probably don't need advice from me! Yes, track planning SW is irreplaceable for working out ideas without drafting tools and paper, let alone committing materials and effort to build something, to see how it will work. On the other hand, I spend way too much time designing my "next" HCD layout on my computer. And it sure is fun reading, discussing, and railroading vicariously on the amazing layouts (built yet or not) with their builders here.