We currently have Sharepoint Online. I am aware that users without a license can still access the site if the users are added into a Sharepoint group. The users are all internal and non are outside the domain. We have ADFS setup for the users. So my question is... do we really need to purchase additional license for the users even though we already given them access into the site? If the rule is that it still requires us to purchase a license per user... is there a way that the users could just View/Read the site (not edit) without the need to purchase a license per user?
External users (using Microsoft Accounts or other Office 365 tenants) are used for non-employees/contractors. Otherwise, for your internal employees, yes you need to allocate a SharePoint Online license, such as SPO P1, P2, or another license that bundles SharePoint. The access rights you grant has no impact on the license acquisition requirement.