Reduced fighting ---probablyCastrated and tailed lambs can definitely have a better life experience by reducing fighting, fly strike and unwanted pregnancies. It is also very sustainable.
Fly strike is more down to dirty /woolly tails than tail length ---there is research from Merinos showing that the longer the tail the less strike
Unwanted pregnancies---managed by better management?
I'm not against castration/tail docking as i think they are useful tools to have but i am for increasing welfare (if possible) and re-examining practices (tradition plays a large part in both these practices)