ROLLING OUT: SharePoint Online team sites + Office 365 Groups & Pages

Each app has a main use case, and certainly some overlap in cases - or hand off from app-to-app when appropriate. SharePoint app = sites & portals access. OneDrive = files management. Groups app = interact with group conversations. The portfolio of apps is always being evaluated and adjustments of how they interact and overlap are expected. Hope that helps, Mark.

Good question! Robert Woods 

Not everything is created from SharePoint and more often OneDrive tends to be a starting point for a document lifecycle and eventually will end up in a SharePoint team site or even in Groups! Overall for me they are the endpoints to get to the information relevant to me.

I've highlighted the key differentiators between each of the apps.

OneDrive app
- lets you work with your personal (OneDrive) and work files (OneDrive For Business)
- access all your OneDrive files and files shared with you

SharePoint App
- access to intranet
- quick access to your team sites and the people you work with
- to see the site activity, sites you frequently visit and the sites you follow
- share a site (subject to permissions)
- access to recent and popular files spreasd across multiple document libraries

Outlook Groups (Office 365 Groups) App:
- Easily participate in group email conversations
- Work together using the shared team OneNote's notebook
- Discover and join Office 365 Groups relevant to you

Hope this helps.