Custom Reports and Dashboards are very similar. Both give you an overview of your traffic and let you see patterns.  A dashboard is meant to give you a more basic overview, while a custom report lets you deep dive and create a view that gives you more control over what you want to see.  

Think of the dashboard as a summary or snapshot of your activity, while the custom report is more of an extension of what you see under the Audience, Acquisition, Behavior, and Conversions tabs.  Many times in these standard reports the information you want is buried several clicks down within the interface. Custom reports allow you to pull that to the front and include just the information that you want to look at.

Many of the elements that you can place on a dashboard have a limited amount of customization that you can add – how many fields to monitor, which fields to watch, and so forth.  Custom Reports gives you greater control, allowing you to put a larger number and a greater variety of metrics within a widget.

One important distinction to make between reports and dashboards and Data Studio is the ability to use Segments.  Segments can be applied to any custom report, while they cannot be applied to dashboards of Data Studio views.

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