The fact that he has been reloading for 30 years and has never done that step shows that it is clearly not "necessary"..... but that's not to say it isn't beneficial.

It also depends on your trimmer- how clean it cuts and the bullet you are using. Some boat tail bullets load fine and upon pulling to inspect them they showed no jacket damage. Other bullets you can feel hanging up and then a little pop as they overcome the resistance (which can't be a good thing). It is a step that I do- but previously didn't- and it's not a night and day difference. Also- in neck tension testing I can not make it be as big of a deal as everyone tells me it is- when isolating only it. But still strive for consistency.