The purpose of deliverance is to help people relate to God in an area in which they are not correctly relating to Him. God thinks relationships are so important that He sent Jesus to die on Calvary for us so the relationship mankind originally had with God could be restored.
This is also the purpose of evangelism which is the restoring of people to a salvation relationship with God.
These are the reasons God gave us the authority to deal with Satan and why we must always be ready to tell everyone why they need Jesus as well as what He has done for us and them.
These things should be a natural expression of God's Love in us.
Another expression of God's Love that is a mark of a Christian is to help those genuinely in need when God tells you to help them and not because you feel guilty for not helping them or you feel they need help. If God does not tell you to help them then you are being a bad steward of what He has given you.
Deliverance is also a form of helping people and is a service God has given us to perform for othres so we need to know how to do it.