constant light?

What is the purpose of the 6 in 18/6? I've seen some grow guides that said you could leave the lights on all the time during veg. Wouldn't constant light lead to faster growing and then just switch to 12/12 for flowering? Are there any potential problems with this?

I'm planning on using CFLs so I don't think leaf burn or drying would be a problem.

Thanks.

im growing 24 hours with some they are fine i dont think im gonna do it any longer then the first three weeks but im only experimenting with it so dont believe me 100%

it is recomended to give some darkness for plant. when i cut clones they are under 24 hour light untill 1 weak after i see root then i cut to 18/6...somw strains will do better then other with this like auto flower strains you never put on 12/12 always 24 all the way threw

I'll say it like this, 24 hour light is artificial, 18/6 is more natural. Plus roots grow in the dark & darkness is natural, plus you save on electricity & light life.