A lot of people still run C02 the whole way through, but I believe it's more strain dependent.
For example:
If your running more indica dom strains that don't stretch much... you shouldn't worry as you may even benefit from spreading out a more dense cola... It could help prevent molds and mildews since the cola would have a bit more internodal space.
Sativa dom is another story, and especially the case with OG dom hybrids like Jesus OG... you can see in TRays that it has the ability to stretch wayyyy out. Not that its a bad thing if you have the head room to spare. But if your stretching out too much, your going to have a longer cola... which may be extra floppy and you may be able to supply as much light intensity to lower budsites. Even on MG's Jesus OG's you can see that having been topped the internodal spacing still spreads out fairly wide, which is why i presume he is keeping the light intensity high, and Co2 low.
Hope that doesn't just confuse the shit out of you, RB.
edit: Sorry for getting carried away with that that on your thread MG!