Host Groups In Foreman?

Issue

• I am trying to install openstack Environment using foreman. I want only four nodes : Deployment foreman server, Controller, Compute and Storage.

But I am confuse about the host groups which you mentioned in the foreman GUI: Controller(neutron), Compute(neutron), Controller(nova network), Compute(nova network), Neutron Network.As per my understanding , each group should have separate node.

So, My Questions are :

1. Difference between Controller(neutron) & Controller(nova network) host group?
2. Difference between Compute(neutron) & Compute(nova network) host group?
3. In what conditions, we have to use neutron network host group?
4. Can we use only controller(neutron) and compute(neutron) without neutron network host group. will that work?
5. If 4th point works then where will neutron services run, do we have to define externally?