For me, it's no sag under the bar. No tighter than what it takes to get that, and not a smidge more. Short bar or long, same same.
This is how Stihl saw manuals teach you, and how I learned from a Stihl trainer.
Some people will run their 36" bars and up a little slack, allowing tool-less re-railing of a thrown chain, by bending the bar over, and working the chain back on, sprocket first, then the nose, then the sides. Not the gentlest on the bar..
Some people want to tighten up a slack chain that is hot and expanded from being run dull, low lube, twisting in the cut. The answer is to clean the oiling system, check the oil output, and sharpen the chain.
Stihl are 'pre-stretched' and are harder steel that stretches less than Oregon and others. Over the lifetime, Stihl needs less tensioning. New chains need tensioning the most after a little running.
Way back in the day our conservation crews worked with the the Exotic Plant Management Team of the NPS on Joint projects, sometimes. They used to have their chains stretch from lots of sand in the tamarisk/ 'salt cedar' bark, and eventually ran out of tension-ability, though the cutters were basically new. They would have to pull a link and re-loop it on 28" or so bars, maybe 24".