It's a hobby you can take as far as you want to; everything from the simple circle-around-the-tree at Christmas to warehouse-sized, meticulously-detailed layouts that look like the real thing shrunk down.
I've seen numerous photos of models where it was nearly impossible to tell that you weren't looking at a photo of the real deal.
I think that's what Renegade is going for. He is collecting the cars and engines, now, but has great plans for the future with a complete lay-out.