There are several types of SharePoint sites available. These include Teams-connected sites and sites that are standalone. Functionally there is little difference since they have the same basic features, however they are different in terms of how they behave.
A Team-connected SharePoint site is automatically created when a Team is requested. Existing standalone sites cannot be "teamified".
Here are the major differences between the two:
If the real-time group chat function is valuable for completing a project, then it makes sense to use Teams. Teams is very collaboration focused. If you are not going to use the group chat, then it is recommended to use a stand-alone site. It is also possible to move content between sites, so that a group could use a Teams site for project work, but have a stand-alone site for "authoritative" documents. Something to consider, but this will require proactive governance and maintenance.
For more details on the differences or on what to use when in M365 please see:
https://utoronto.sharepoint.com/sites/SPLearn/SitePages/Information-Management-and-Office-365.aspx
U of T Terms of Use – Microsoft Office 365 Teams
http://office365.utoronto.ca/wp-content/uploads/2018/07/Teams-TOU-20180703-PDF.pdf