If you and your neighbor have decided to share a vacuum cleaner, the potential size of your sharing group is probably not a concern. But if you want to leave open the possibility that the group will grow or shrink, then group size is something you may want to discuss ahead of time.
What should the minimum or maximum group size be? It depends on what you're sharing and how often you'll need to use it, among other things. For example, if you plan to share a car with two other people, and you know that you'll need to use the car several days a week, your group probably can't grow. On the other hand, if you'll need to use the car only a few times a month to do major errands, you could share with a much larger group.
Large and small groups offer different advantages. If you aren't sure what size group will work best for you, consider whether any of these benefits are especially appealing.
On the other hand, small groups:
EXAMPLE: A small group of neighbors form a tool and toy sharing group. Together, they buy a shed to put in the backyard of one neighbor, Ubie. Each households has a key to the shed and uses it to store items they are willing to share. They decide to keep their group small, and write this in their sharing agreement:
" We agree to limit the size of our group to six households. By keeping the group small, we will be less likely to lose items and will not worry about lending our belongings to people we don't know. In addition, Ubie prefers to limit the number of people who enter his backyard."