I'm on my first playthrough of Space Age currently and while I've got something fairly complex on Nauvis with multiple stops and interconnects and loops and a half dozen or so trains... a lot of my needs on other planets are just point-to-point single train transfers. e.g. running a line out to a scrap patch on another island with millions of units of resources on Fulgora after exhausting the initial scrap I mined out. I don't even need multiple cargo wagons let alone multiple trains to max out my factory's input belt capacity there at the moment... Could the whole thing be more efficient? Oh yes -- but sometimes simple is good enough, and not having to build loops before I got the deep elevated rail support and/or foundations helped tremendously!

I think I was probably supposed to figure out the double locomotive thing in the train tutorial -- I don't remember there being loops on the track there... -- but I'm pretty sure I'd already built at least simple factories on everything but Aquilo before I realized it was even an option. :p