Ditto what djfishygillz said. Add to that the ease of purchasing one adult sized cage with accessories that fit (uvb light and hood, making drainage, blah blah). Some people keep babies in huge cages with a feeder cup, but I have enough trouble finding my chams in their cages right now and they're def. big enough. If I stuck a little two month old in a 2X2X4 I'd spend hours searching and assuming I'd lost him. Also, for me, once I had one cham that was sub-adult I wanted another of similar age, for future breeding but also so I could buy one size of crickets and feeders. If I get another, I'll do the same if possible.
yeah my two panthers are still young babies so is my baby veiled. my 7 month old ousta is a juvinile around 7-8 month and he is already bigger then your adult veiled. i prefer babies over older ones do to the fact they get use to you and know you are their provider. colors really don't mater to me unless its a panther chameleon. but if you want to get a baby and enjoy a long journey i say this if you hold them when you put them back in their cage put them on the ground and let them climb up on thier own in their cage cause they are fragile and they will be less likely to lose footing and fall to the ground.