The Preview Features setting in SharePoint admin center gives you the ability to enable or disable the following service integration scenarios:
where SharePoint integrates with a service that has a different Service Level Agreement (SLA) than Office 365
where data leaves SharePoint compliance boundaries
Note: The Preview Features setting isn't related to the first release option which allows you to receive new updates and features as they become available. If you're interested in signing up for that, see Office 365 release options.
Specific features that depend on this setting
PowerApps and Flow integration
You can create custom solutions by integrating PowerApps or Flow with your SharePoint lists. When you do this, SharePoint data might be used outside of your SharePoint environment. If this is a concern, select disable preview features for this setting. If you disable preview features, the PowerApps and Flow buttons won’t appear in SharePoint. See the following links to learn more about how PowerApps and Flow work with SharePoint.
Power BI integration with Excel Online
When you use Power BI, your data is sent to the Power BI service. If you have implemented compliance policies for your SharePoint environment, these policies won't extend to the data as it's processed in Power BI. If this is a concern, select disable preview features for this setting.
Important: When you disable preview features, your users will no longer be able to use Excel Online to view and edit workbooks that rely on Power BI.