Before we go around casting out demons, we need to be sure the person we are casting the demons out of has accepted Christ. We need to be sure that the Holy Spirit is living within them. If you cast out demons just because you can, and the word says you have the authority to do so, you need to be responsible with what you are about to do. If the Holy Spirit is not living within that person, then that demon will just wander around until he finds 7 of his buddies, and then come back to dwell in that person, and the person is worse off than he was. And the demons can do that, because the house is empty.
However, if that person has accepted the LORD as their Savior, and the Holy Spirit dwells within them, then the demons have no place to reside, and will have to move on to another dwelling place.
Matt. 12 v 43-45.....When an unclean spirit goes out of a man, he goes through dry places, seeking rest, and finds none. Then he says, I will return to my house from which I came. And when he comes, he finds it EMPTY, swept and put in order. Then he goes and takes with him seven other spirits more wicked than himself, and they enter and dwell there; and the last state of that man is worse than the first. So shall it be with this wicked generation.......
Just because we have been given gifts of the Spirit does not mean we are to use them unwisely. Don't get filled with the Holy Ghost, only to go around scaring everyone with your tongue speaking. If there is no understanding, what have you accomplished? Don't think that you are any better than another of a different denomination because you can speak in tongues, or you can heal, and they have not yet received those gifts. We are all after the one goal, that Jesus had in mind when He came to this earth, and that is to bring all His children under one authority. We may not worship in the same buildings, but we are of the same house and we must stand together.
Matt. 12 v 25....But Jesus knew their thoughts and said to them; "Every kingdom divided against itself is brought to desolation, and every city or house divided against itself will not stand.".......
Therefore use your gifts wisely!