Equipment permissions are used to define what boats that members of a particular group are allowed to reserve for practices and private reservations. As with group permissions, users inherit the equipment permissions of all of the groups they are a member of.
Using the groups combined with equipment permissions, you can control which users are allowed to reserve. For example, if your organization requires members to pass a flip-test before they are allowed to row a single outside of practice, you can create a group called "Certified Single Scullers" where you add all of the club singles to that group's equipment permissions. This group would have Allow Self Join set to "No" to keep non-certified scullers from joining the group without passing the flip-test.
We also strongly recommending creating a (or using the default) "Coaches" group that is granted equipment permissions to checkout all of the boats that may be used for practices. Doing this will allow your coaches to add those boats to practice lineups.