Staff user accounts are intended for employees at your agency. Client user accounts are intended for your customers. Both allow you, as the agency account owner, to restrict which data a given user is allowed to view, and which actions they can take within the dashboard.
For BOTH Client and Staff user accounts you can:
Grant access to view any subset of Clients in your dashboard.
Permit or restrict access to any given area of the dashboard. (Note: This is a global setting, meaning that it cannot be set on a per Client basis)
Email or login as the user from the "User setup" area of the admin console.
Also, NEITHER ever has access to billing or white label settings.
Staff Accounts:
Depending on your chosen settings, can also add/edit/remove other user accounts, with the exception of their own
May edit/modify their view of the dashboard and settings on both the home screen and within Clients for which you've granted them access
Can access our customer support and knowledgebase
Client Accounts:
No ability to view user accounts console
No ability to edit/modify the dashboard or any settings or filters. YOU choose EXACTLY what they can or cannot view when they log in.
Note: If you have an important client who needs the ability to manage/edit/modify their own dashboard setup, you'll need to create a STAFF account for them and carefully choose their access restrictions.