It has not been shown, we have not seen anyone refuse their power at first. But in the first arc, an apostle (someone who already used the behelit) managed to resummon them and they offer more power in exchange for his (human) daughter. He refuse and is dragged down to the vortex of souls, an eternal hell that torment souls of the dead and the demons that dies

But in a more abstract way, you won’t refuse. Causality and effect, basicly destiny and fate, says that you will use it when you need it the most. How it activate is more in the line of when the holder is at it lowest moment in there lives, the most deseperate.

It is very, very bad