I believe it to be safer because a newborn calf would be restrained between your legs or under your knee while the mother is pacing behind you shaking her head, literally. I do "work" newborns, I'll help dry them if it's cold/wet, eartag them if they are heifers so I can register them in case they become replacements. But otherwise if they're nursing, I'm happy to leave them be.
Aside from being arguably better for the animal, It's honestly easier to band later. We all know separating your calves at weaning is a bit of a production sometimes, getting everybody separateted and moved. I find at that time when I'm managing the herd anyway it's a good opportunity to run the calves through the chute, vaccinate, band all the bulls, pour-on, tetanus shot. You've gotta work them anyway, if you vaccinate prior to weaning most say to revaccinate at weaning.
And a day (or even just hours) of lameness would be a lot more detrimental to a newborn than a 600 lb calf.
Wouldn't you rather throw a band on from a palp cage then in the field, on top of a squirming calf.
I'd like to add, many banders, most in fact, do not tension the band properly leading to the complications I image some have seen. If green cherio bands in particular. I promise I'm not a spokesperson but Calicrate uses a loop of surgical tubing that is ratcheted to an exact tension and then crimped in place.
Just my two-cents.