The main comparison they are making in this article, as I read it, is
1) Castration "under 3 months of age" (not necessarily right at birth)
to
2) Castration at weaning or 500lb or heavier.
The article also says "Castration at less than three months of age is a reasonable alternative to castration soon after birth."
Personally I like the "3 months of age" time. Surgical cutting at about 3 months old then letting them out on clean green grass to heal quickly lets you get them all at the same time. "3 months of age" would mean calves born in April would be cut in July. They can be run thru the chute and all done at one time, safely, along with weighing, shots and poured. They will then be mostly in the 2 to 3 month old range.
This also avoids trying to catch newborn calves and banding them, often in springtime mud... Granted however it might be easier for some operations that calve in a confined area in the spring then let the calves roam large stretches of rangeland over the summer to get the job done right at birth than to try to round them all up in July.
If you have some keeper bull candidates and need to let them grow out a bit would be the main reason I can see for delay for breeders.
Thanks for the link, Dun.