Yes, you can have a primary site with distribution points, without having secondary sites.
Consider installing a secondary site if any of the following conditions apply:
You do not require a local administrative user for the site.
You have to manage the transfer of deployment content to sites lower in the hierarchy.
You have to manage client information that is sent to sites higher in the hierarchy.
Consider deploying a distribution point instead of installing another site if any of the following conditions apply:
Your network bandwidth is sufficient for client computers at the remote location to communicate with a management point to download client policy, and send inventory, reporting status, and discovery information.
Background Intelligent Transfer Service (BITS) does not provide sufficient bandwidth control for your network requirements.
The advantage of using distribution points over secondary sites is a less complex hierarchy, and simplified administration. With distribution points at a remote location, the clients will pull content from the distribution point, rather than pulling content across the WAN. But the clients still have to go across the WAN to pull policies, and send status information (back to the primary site). This is typically not that much traffic, but if the remote locations bandwidth isn't sufficient for pulling policies and sending status information, then you would want to set up a secondary site. With a secondary site at the remote location, retrieving content, policies, and sending status information would all be local traffic. The only traffic on the WAN would be replication between the primary and secondary site.
Let me know if you have more questions,