SharePoint is the shared filing system in Teams that everyone can access.
When you save Files in Microsoft Teams then you are accessing a SharePoint site. Teams creates 1 SharePoint site for every Team automatically and these sites have standard read and edit permissions for that Team.
If that is all you need, then skip this offer.
But if you need more flexibility and have lots of different Team member permission levels, then you will want to customize a system that fits your specific organizational needs and SharePoint will help you do that ...