Pro Sites and Domain Mapping


I'm a little confused on the domain mapping functionality of pro sites.

Is domain mapping built into the prosites plugin or do I have to install the domain mapping plugin:

in order for this to work.

Also, does it matter if I use subdomains or sub directories for domain mapping to work?

(I thought I chose sub domains for my site but it is using sub directories, I know that in order to change it I have to reinstall and I don't want to do that)

Your feedback would be greatly appreciated.