composite API.
<ul>
<li>Multiple REST API calls for single call
</li>
<li>Processing speed can be made faster by collating the subrequests.
</li>
<li>Improves the performance of the application
</li>
<li>No additional coding required at Salesforce. 
</li>
<li>Single call toward API limits.
</li>
<li>Synchronous responses.
</li>
<li>Multiple ways in composite resources work.
</li>
<li>Upsert upto five levels deep relationships.
</li>
<li>Flexible on upserting related or non related records.
</li>
<li>Can do a GET subrequest and the result can be input to next POST subrequest.
</li>
<li>Can handle more complicated and related objects and data.
</li>
</ul>

composite API.

* Multiple REST API calls for single call
    
* Processing speed can be made faster by collating the subrequests.
    
* Improves the performance of the application
    
* No additional coding required at Salesforce. 
    
* Single call toward API limits.
    
* Synchronous responses.
    
* Multiple ways in composite resources work.
    
* Upsert upto five levels deep relationships.
    
* Flexible on upserting related or non related records.
    
* Can do a GET subrequest and the result can be input to next POST subrequest.
    
* Can handle more complicated and related objects and data.

Why Composite Resources