Hi Christopher,
Please see the following description from the bottom of the prices page:
If you operate a WordPress® Multisite Network, for the purpose of maintaining multiple child blogs or sub-sites that you own yourself, an s2Member® Unlimited-Site License is sufficient (e.g. you do NOT need a Network Support License if all child blogs or sub-sites are your own).
In the case of a WordPress® Multisite Network operating as a Blog Farm, you WILL need our Network Support License (e.g. our Network Support License is required for Blog Farms), which includes everything that our Unlimited-Site License provides, plus support for the creation of child blogs or sub-sites; including the ability to restrict the number of child blogs or sub-sites that can be created by your users/members.
If you operate a WordPress® Multisite Network, and your Network DOES make it possible for users/members to create child blogs or sub-sites (in any way), we consider your installation to be a Multisite Blog Farm. Please note, many site owners run a Multisite Network for the purpose of maintaining their OWN child blogs or sub-sites. The term Multisite Blog Farm does NOT apply to a Network that hosts multiple child blogs or sub-sites, all of which are operated by a single site owner. A Multisite Blog Farm (in the eyes of s2Member®), is a Network that makes it possible for its users/members to create child blogs or sub-sites; where one or more of these child blogs or sub-sites is administered by a user/member (e.g. if you offer blogs or sub-sites to your customers, for free or otherwise).