The QUOTA system is the method by which you allocate or restrict resources to a profile.
has certain modules which can be used on that profile. Its the Quota system that determines that.
Eg: If a module can have audio files uploaded to it, its because its in a Quota that allows audio files to be uploaded.
The Quota is the setting, the Profile is the location.
You can have many different Quotas existing in the system, but a Profile can only belong to one quota at a time.