CB Gallery config : Limitations

In the tab videos and photos what is the difference between "Create Limit" and "Custom create limit" ?
Create Limit: Selection of the field to use for item create limit. Moderators are exempt from this configuration -> does this mean that we can create a user field with a numeric value which determines the limitation of the number of photos / videos imposed on a specific user ?
Custom Create Limit -> is the limitation of the number of photos / videos imposed by default on all users if the limit field is left empty ?

You can select a fields value to be used for creation limit. So for example you've an integer field configured as Read Only or not available in profile edit. You can select that integer field to be used as the create limit. This allows for per-user create limits. You can then for example set this field using CB Paid Subscriptions so you can have people pay to be allowed to upload things.

The Custom Create Limit is just a static create limit applied to all users.

Custom Create Limit -> is the limitation of the number of photos / videos imposed by default on all users if the limit field is left empty ?

Empty means unlimited. This can't be used as a means of disabling uploads. You'd use the access parameters for that. So the create limit must be greater than or equal to 1 for it to apply.