A male/female combo will also typically stress out the female pretty badly eventually too, as the male will often want to try to mate as much as possible regardless of whether she's ready for it or not. You could also run into "nipping" problems (when one beardie tries to eat the exterraneous limbs of another), and a host of domination issues.
It's probably best to keep your dragons seperate unless they're both female. Even then, some would advise against it. Although, there has been some success if you have a big enough cage, but I think in most of those cases they were all female.