Which to use - Teams or SharePoint Online?

Microsoft Teams and SharePoint Online are complementary collaboration tools that are part of the Microsoft 365 suite. 

Microsoft Teams is the hub for teamwork. It allows for real-time collaboration, chat, calls, meetings, and file sharing. SharePoint Online is primarily a document management and intranet platform where you store, collaborate, and share information across the organization. 

What happens in the background when a new Team is provisioned?

• Microsoft 365 Group
• SharePoint Online site
• Exchange Online shared mailbox & calendar
• Ties into other Microsoft 365 apps, like OneNote and Planner

Where are my files exactly?

Each time you save or create content in a Team, it is stored in the associated SharePoint site, not in Teams. The exact location depends on which Team channel you select. Files shared in the General channel (the default) will be stored in the SharePoint site’s Documents library, within the General folder. If you create a Team channel called “Project A”, its files will be stored in SharePoint under the corresponding “Project A” folder, and so on…

Who can access or see my files?

People can view and search only content they have access to. Therefore, when you add or remove people from a Team, their access is also added or removed from the SharePoint site and Documents library.

Are my changes reflected?

Yes. The changes made to files and documents are saved automatically in real time. And you always have the latest version of the document, whether you are in Microsoft Teams or in SharePoint Online.

Source: Should I store my files in Microsoft Teams or in SharePoint? An understanding of behind the scenes