Rich, new file and sharing experiences throughout Microsoft 365, now in Microsoft Teams

Allan With Sørensen 

I would use EXTREME caution with advising users to sync libraries. In fact, we tell users to NEVER sync libraries at any level. Ever. Under any circumstances. We've had multiple instances where the users "forget" that the library is synced, decide they don't need to see the content anymore and hit the delete button. At this point, the library disappears from the SharePoint site but does NOT go to the recycle bin. If you're lucky the files might still be found in the recycle bin of the person who deleted the files, that is assuming they don't empty their recycle bin when the computer reboots in which case you have a real problem. We had one group lose almost 10,000 files for several multi-year projects. It was a disaster. 

Users will have the best/most reliable experience with SharePoint and Teams if you use the UI as it was intended. Teams should be accessed via the desktop application or browser and SharePoint via the browser. 

The reason O365 groups are not named Teams or SharePoint groups is because they are larger than just Teams of SharePoint. They span all of Office 365, including Stream, Planner, Power BI, etc. We are careful to consistently refer to them as "O365 Groups" rather than just "groups" as a way to distinguish between a SharePoint permission group or distribution list or what have you. There are lots of good resources out there on what O365 groups are and how to explain them to users - Matt Wade & Ben Niaulin have some excellent blog posts that I included on my User Site under "Learn more about O365 Groups".

The most important part about O365 groups is teaching users NOT to manage permissions via the SharePoint permission groups - That you HAVE to edit the GROUP in Outlook, Teams, Planner, etc.