"As Jesus was getting into the boat, the man who had been demon-possessed begged to go with him. Jesus did not let him, but said, 'Go home to your family and tell them how much the Lord has done for you, and how he has had mercy on you.' So the man went away and began to tell in the Decapolis how much Jesus had done for him. And all the people were amazed." NIV translation
Here, we see the effects of being saved. First, we see that the man did not want to be left behind as he wanted to go and be near Jesus. It is the same with us today in that, when we truly come to Christ, there will be a desire to go and walk with him.
Next, we see that Jesus told him to go and tell his family and others about what had been done for him. That is what we call a testimony and the man went and did so out of gratitude for what Jesus had done for him. He willing obeyed what Jesus told him to do.
Finally, we see that God was glorified and those that heard about what He had done were amazed. There are many, today, that want to take what God is doing and use it for their own glory but that is not the purpose of the miracle or telling others about it.