more potent. fems won't match under the same conditions over time.
cost effective. not so much for the home hobby. we ran regs when commercial cause we could control a lot more including breeding. which ties back in to more potent.
can run your own breeding which ties back to the first two points. only serious growers / breeders will run regs. the rest are simply hobbyists. won't matter how big you think you are.
professional reasons. regs are the gateway to working in the industry if you really want. no one takes you serious otherwise. only if you are a grower / breeder though. if you're gonna be a budtender no one gives a shit. it's like mcdonalds.
also most legal dispensaries are now concentrated on non-fem only or non-auto offerings.
expanding product line if you are a pro, and want to sell seed , all fems and autos are first developed through reg breeding.