A hermie produces seeds. When a female plant (or part) gets pollinated it starts focusing most of it's energy into seed production, instead of THC. So a bud with seed will be less potent than without. It can be smoked.
The real thing that makes a hermie undesirable is that it will almost certainly pollinate other females in the area, making them less potent and full of seeds. Seedy bud defeats the purpose of controlled growing.
I suggest at the first sign of male parts you spray with Dutch Mater Reverse, which will force the plant to revert back to female, provided any sources of stress are corrected first. If the plant is too far gone, or you can not find the Reverse spray, you best bet is to kill it.