You use default, explicit, derived and tracking quotas to manage disk usage in the most efficient manner.
How default quotas work
You can use default quotas to apply a quota to all instances of a given quota type. For example, a default user quota affects all users on the system for the specified volume or qtree. . In addition, default quotas enable you to modify your quotas easily.
How you use explicit quotas
You can use explicit quotas to specify a quota for a specific quota target, or to override a default quota for a specific target.
How derived quotas work
A quota enforced as a result of a default quota, rather than an explicit quota (a quota with a specific target), is referred to as a derived quota.
How you use tracking quotas
Tracking quotas generate reports of disk and file usage and do not limit resource usage. When tracking quotas are used, modifying quota values is less disruptive, because you can resize quotas rather than turning them off and back on.