When I was first a nurse, (in the mid to late 70s), the Evening shift was the shift that the 'newbies' and the young nurses had, (i.e., those in their 20s). It was okay if you were a partier, you could hit the bars and/or parties after work, go home and sleep it off before you had to go to work the next afternoon.
But forget about ever seeing your family in the evening in any meaningful way. Later when I became an ADON at a LTC facility I found that the hardest shift(s) to cover is the Friday evening shift.
There are other advantages to an 8 hour evening shift, only one meal to deal with, hs care and pre-op baths, ect. Usually less exams, med passes, and procedures, but I would never go back to five days a week 3-11 shifts.
A 12 hour shift usually allows for more actual patient interactions in a somewhat less intense, gotta get tasks and paper work done type of situations. More days off is a big plus. (It has got to be advantageous to the 'suits' also, or they would never have offered it, or allow it to continue).
The fact of being tired after 12 rather that 8 hours I think is a negative I guess, but I remember being much more tired and stressed out about how I am going to get all my work, (and paperwork), done in 8 hours that seemed to be a day-to-day thing, five days a week "once more into the breech my friends, and fill the wall with our British dead", than I usually feel after a 12 hour shift.
The complaint about not being able to eat or 'go to the bathroom' for 12 hours as opposed to 8, well...that is a lack of self-assertion and allowing yourself to be a martyr than a real objection to 12 hour shifts
But, there will never be an abolishment of the 12 hour shifts. Too many 'working stiffs' like it..Too many employers see the advantages for it for it to ever to be done away with.