It has nothing to do with System Restore.
It presumably has something to do with restoring the PC to a factory state. It could be the PC manufacturer's tools of some type.
What is in it?
If you are positive you can do whatever restoration you need to do with the discs you made, then you wouldn't need it as far as I know.
How easily you can add the space to C depends on what your Disk Management picture looks like. In one case, you can do add it to C from within Windows. In another case, you would have to use a third party application.
That's why I asked to see the picture.
Your original post says you already deleted it.