I've volunteered to deal with the IT of a small non-profit, but I have no real experience with Microsoft 365. I've had a play and I'm generally happy with all the tools and setup, but still have some confusion about how the licenses work.
They have about half a dozen PCs, all of which have device based Windows 10 Pro licenses (i.e. came with the PC when new). They also have a 10 'Microsoft 365 Business' licenses and 25 'Office 365 Business Essentials' licenses. Some users need proper office, so they get assigned the full Business license, the others can just have Business Essentials in order to have access to SharePoint/OneDrive and email. So far all of this can be done without AzureAD or anything complicated, I can have local users and they can sign in Outlook online, OneDrive (everyone) and use Office 365 Desktop applications (just those who have a license) .
Next step, in order to avoid needing to setup local users for everyone on each PC, I want to use AzureAD, and then join each PC to it. That's when the licensing gets confusing. The user that joins the PC to AzureAD seems to then supply the license for Windows (in activation settings it goes from standard Digital License to Business Subscription), even when a user who only has Business Essentials (no windows license) is signed in to the PC. Same with Office 365, when a user with only Business Essentials (no Office 365 desktop apps) is logged in they seem to be able to run Office 365 just fine, they are logged in as themselves, but the Account page shows "Belongs to" and the user that joined AzureAD. It looks like, as long as someone with a full Business license joins the PC to AzureAD then anyone logging on with a lesser Business Essentials license can get the benefit of Office 365 Desktop apps. That doesn't sound right.
Also, having joined AzureAD the devices seem to have become enrolled in InTune, which also requires a license. The user with a Business license has a license for Intune, but what happen if a Business Essentials users joins the PC to AzureAD, or the fully licensed Business user never uses the PC again after it's been joined?