1) If you want to deploy a openstack private cloud (whether its single or multi node) Neutron service is required. I mean it provides network connectivity to your VM's.

2) It enables Network-Connectivity-as-a-Service for other OpenStack services, such as OpenStack Compute. Provides an API for users to define networks and the attachments into them.

3) If you want to deploy only swift (object storage) neutron is not required. You can integrate swift with keystone for authentication and authorization.

For more understanding go through this conceptual architecture

http://docs.openstack.org/admin-guide...

Regards,
RHK