The RAF early on realized their bombers lacked adequate protection from fighter attacks and the bombers also didn't have the equipment for an real "precision bombing". Hence resorted to night missions for the bombers and that meant area bombing of a general target.
The USAAF thought that with the Norden bomb-sight they could perform "Precision Bombing" ~ 'drop the bomb into a pickle barrel from 30,000 feet'. Turns out not quite so precise. USAAF bombers were better armed for fending off fighter attacks, though they still needed to have friendly fighter escorts as well. And USAAF daylight bombing usually could remain somewhat concentrate on the target, if the weather was clear, still in the large formations they flew, there was quite a bit of spill over out of the target area.
Railways can be knocked out significantly if hitting the marshaling yards. Post bombing photo show such. Biggest problem for Germany was scrounging up the steel and making replacement rails from it. Plus scrounge up the labor and wooden ties, etc. If all those ducks got in a row, might take weeks to months to rebuild, depending on extent of damage. Not to mention that often some locomotives and rolling stock would be destroyed as well. Destroying rail yards was more for sake of constricting movement of troops, weapons, and material.