Google by default uses sampling technique in order to process data faster. If you are still unaware about what sampling means then have a look at this article about data sampling in GA.
The Unsampled Reports feature provides accurate analysis of large unsampled data sets and also provides a way to integrate the API into your Business Intelligence (BI) system. This makes retrieve unsampled data easier and provide accurate metrics that support your critical business decisions.
For a full documentation on how to retrieve unsampled data using Management API, please read –
https://developers.google.com/analytics/devguides/config/mgmt/v3/mgmtUnsampledReports
Also See:
How to Create Goals in GA?
Google Analytics Interview Questions and Answers
New Google Quick View Button on Mobile Search Results
Query Highlighting on Google Search Results
How GA Collects Data From Mobile Apps