Never owned one and don't see a need for it with my cannabis. OPC (other people's cannabis) has shown me what folks are talking about though. I've run across some very tough flowers in the past.
Well grown cannabis doesn't need a grinder. You gently push the bud against the side of the bowl, cover the broken bits of frosty cannabis with your thumb and gently twist/pull the single central stem out. Push the pile into the bowl and you're done. Rolling is close to the same, just a gentle roll between the fingers crushes the bud into little frosty bits. I rub the *sticky* on my fingers into little hash bits and the remainder helps roll the joint easily. ;)
No, we're not talking about over-dried flowers, just well grown.
*Need* scissors? Too much nutrient and/or silica during flower. Should be very little stem, without any side branching in the flower (controlled by nitrogen/light density).