Like most anything else, the pre-twisting can be done incorrectly.
I've run across a high number of failed connections where the wires were pre-twisted to the point that the diameter of the twisted conductors was large enough that the wirenut couldn't get any purchase on the connection. The wire nut in this case serves no more purpose than that of a piece of tape. Very often the wirenut has fallen off as soon as I touched it.
Also, I've found connections where 1 or more of the conductors has slid back from the rest when twisted and makes poor contact or none at all.
I've never been a "pre-twister", and only know of a couple of connections I've ever had fail.(in 30+ yrs)
My big gripe is with the use of wirenuts out of their listed range. It seems like some people think that they only come in one size...Red. Anything from 2-#18 to 7 or 8-#12 get stuffed in them. (The yahoos that overfill them often wrap them with tape to keep them from falling off). This has been the singlemost often cause of failures I've run into personally, and most commonly have been on neutrals because more of them are tied together in a box on multiwire circuits. (Naturally, because this is the most destructive connection to lose!) [Linked Image]