I think it's a couple things... like Indicas can take a couple MONTHS to reveg. And if you are doing things in an organized fashion, you would already have a backup mother of the same strain kicking around to keep the genetics going.
IMHO, the main reason that you would want to reveg a plant would be if it turned out to be some fabulous pheno that you didn't have a copy of saved. Like I've got to reveg one of my girls over the next couple months because I never took cuts off her and she turned out to be a REALLY desirable plant.
Some people DO reveg for a second harvest off the same plant but I would be too afraid of herms at that point, plus if you're running clones, you actually don't save any time.