Acts 19:
13Some Jews who went around driving out evil spirits tried to invoke the name of the Lord Jesus over those who were demon-possessed. They would say, “In the name of the Jesus whom Paul preaches, I command you to come out.”
14Seven sons of Sceva, a Jewish chief priest, were doing this.
15One day the evil spirit answered them, “Jesus I know, and Paul I know about, but who are you?”
16Then the man who had the evil spirit jumped on them and overpowered them all. He gave them such a beating that they ran out of the house naked and bleeding.
These were people trying to cast out demons in Jesus Name who hadn't professed him. They were trying to 'use the power' without being plugged into the power source.
The overall thing is, where does the glory go? Any and all acts of the Holy Spirit will glorify the Christ. Anyone who tries to bring glory to himself, or anywhere else, by these things is false.