Shortly, cannabis is one year plant. It sprouts, growing on veg, blooming (producing seeds in nature) and dies. Re-veg is something artificial, not natural to a plant. Some plants will do re-veg some simply won't. After you switch your lights from bloom 12/12 to 20/4 or 24 veg mode you have to wait 3-4 weeks only to notice/figure out weather your plant will do re-veg or not. This is a massive stress for a plant and it can turn into herm, being male/female same time. Re-veg plant brings a way smaller buds if any .... sometimes really small, only pop corn buds ... etc, many things can go wrong and usually go wrong as this is very un-natural for cannabis to re-veg. 

Reveg for clones and they will grow like any other clone. Never reveg for bud or you will probably be disappointed