Well I haven't read anything but it would be logical that the plant is expending energy to grow taller than it needs to rather than using that energy to grow bud. This would require that the plant had a set amount of energy throughout the grow and wouldn't produce more to stretch.
Really stretch just makes it hard for the indoor grower if head room is limited. Also lights won't penetrate as far into a tall plant.
Just my thoughts. Can't say it's a bad thing or a good thing.
Stretching doesn't hurt and it's a natural process that many breeders tried to limit looking for phenos that don't do it that much. Still, you won't find a strain that just doesn't stretch.
It can be bad if it's caused by plants being bunched together competing for light or light being too weak or far away, the plant will grow tall, thin and weak stems that may not be able to support buds or even themselves.
As others mentioned, stretching doesn't really hurt anything, as it is natural to the flowering process. It can be an issue with headspace, as mentioned, and I don't particularly like it because it causes the nodes to spread out, making it harder to achieve a large cola. Instead you end up with spread out buds.
Also, the less the plant stretches, the better light penetration you can get to lower bud sites in indoor grows.
Thinking about this logically, it would make sense that if the plant stretches, then it will be concentrating on upward growth rather than bud growth and thus reducing the overall yield.
Whether or not that is true; I don't know, but it's logical.