* I disabled 90 degree turns in OTTD-JGR as a concession to realism. What do you do. Also, Master Hellish in his videos makes a good point that tight multi-level junctions and long trains don't really mix; as the whole point is to keep everyone rolling.
It's not a matter of short or long trains, but of speed and effiency. My trains are always 3-tile for local trains, 5-tile for the majority of them (which is mainline) and 6-tile for high-speed trains. So for a local line that I want to run at full speed, I will have to put 3-tile track curves, 5-tile for mainlines and 6 (or 7) tiles for high-speed so that trains don't slow down.
I still have to use 3 or 2-tile curves sometimes on all types of lines (except high-speed) but never 1-tile - never do this one, it slows down trains too much - as I need to keep my trains at a good speed for them not to slow down others. That's how one also manages to have only cloverleaf or flying junctions, just like me.