This is interesting. Let's take the case of an imaginary bodybuilder, natural bodybuilder to narrow it down, who competes yearly and moves up in weight each competition.
If he's dieting to competition lean every year, but his weight is moving up, there seems to be a very small margin for holding a 'bulked' weight.
Naturally, there's going to be a difference between a guy who's moving up in weight to the tune of maybe 3-5lbs of muscle per year then the guy who goes straight through bulking to put on the mass, due to the time spent dieting and not gaining.
I'd like to see some data on this, but reason would dictate if a 'hobbyist' bodybuilder, I mean no offense with the term just somebody who does it to do it and isn't interested in stepping on stage, who does a fairly reasonable cut where just getting visible abs is the goal and not glute striations, therefore the muscle loss dieting would be minimal if done correctly, wouldn't have to worry about holding a bulked weight for any amount of time.
As of now, this holding the weight thing is in the category of 'bro-science' to me and I would attribute its prevalence due to the loss of potential lean mass gains by dieting instead of bulking for ~3-4 months out of the year.
Taking the case of Shelby for example, who's been competing for awhile, from start to finish he got huge, but if you look at his pics from year to year there are only small differences.