Thanks for reaching here! You may want to know that Data In is the amount of incoming bandwidth consumed by the app, in MiB.
Apps that are hosted in App Service are subject to certain limits on the resources they can use. The limits are defined by the App Service plan that's associated with the app.
Also, trying to understand if you are facing any problem due to high Data In?
Suggest you to Enable application monitoring for Azure App Services hosted applications:
You can use Azure Application Insights which collects telemetry from your application to help analyze its operation and performance. You can use this information to identify problems that may be occurring or to identify improvements to the application that would most impact users.
You can also access the Application Event Log, use the Diagnose and solve problems blade in the Azure portal:
In the Azure portal, open the app in App Services. Select Diagnose and solve problems.
Let us know.