The Misconception
There is a popular misconception amongst some SharePoint folks that Teams and SharePoint aren’t particularly related.
This point of view can be misleading, as there is, however, a not-insubstantial overlap.
Microsoft Teams – amongst playing many other roles – is a window into the SharePoint world.
Where Teams and SharePoint meet
Most know that the the contents of the Files tab is hosted in SharePoint.

Indeed, when you create a Team, you also get a linked Site Collection created for you in SharePoint. Every time you create a Channel, that becomes a Folder in the Team’s Shared Documents Library – hosted in SharePoint.
SharePoint is also the home of:
- The Wiki app – its content lives in special hidden Lists in SharePoint

- OneNote Notebooks – they’re stored in the Site Assets library of the Team

- The SharePoint Document Library app for Teams – use this to bring any existing SharePoint Library into a Tab in your Team

- The SharePoint Pages / List app for Teams – display SharePoint content pages, or interact with content in SharePoint Lists

- The forthcoming Microsoft Lists app – which we are all very excited about! 😊
The Teams Continuum
The Teams-SharePoint continuum extends to Outlook Groups as well.
Teams brings together many other elements of the Microsoft 365 world: Planner, Power Apps, Power BI, Flow, Forms, Groups… and wraps those up with its own chat, conferencing and telephony features.

SPFx Apps for Teams
All this is before we venture into the world of third party Teams Apps. SharePoint Framework (SPFx) developers can write applications for Teams by building SharePoint Web Parts.
One example, is our very own Aardvark Sales for Teams:

In our app, all your data is stored in SharePoint Lists in the Team’s Site Collection, and never leaves your tenancy.
Instead of framing the tools in terms of “Should I store files in SharePoint or Teams”, perhaps the question should be, “Should I surface content stored in SharePoint through Teams”.
Summary
Teams !== SharePoint
Teams ∩ SharePoint
Teams ❤ SharePoint