[Multi-Domains] Do i need Domain-Mapping, if i got Multi-Domains?

Hey, i would like to build a community network. User shall be logged in, in whole network, once they loggin in anywhere. Looks like both: Domain-Mapping & Multi-Domains do have options for this, right?

Do i need both for my project, or is one of them enough?
I prefere Multi-Domains. When i use Multi-Domains, i need to install Domain-Mapping aswell?