If you are an IT manager would you hire an independent consultant for deploying a projects at you department?

There is not a simple Yes or No answer as it greatly depends on the nature of the project. But as a rule I would say if the project involves great Change Management tasks then i would not go with an independent consultant. Since such projects involves aspects that affect persons and to ease the change they need someone they know and can trust so a resource from the department would be my candidate.

However, if the project does not have that much change management then i would go with an independent consultant.

I hope that i understood your question correctly and my answer helped you.

Yes.  In IT life, we need consultancy services in most of the projects like ERPs.  Implementing ERP solution for any enterprise is a gigantic taks and needs proper planning, skills, resource management etc. etc.