It’s a good practice to reduce the number of files by combining them into one file using bundling to increase the website performance.
But the issue with this way , that each time the page is loaded , bundling will occur at run time to combine these files into one file and this could affect the performance in case you have heavy load or visits in your websites.
I did a performance test against SharePoint website (10000 load test within 1 Min) using loader.io and the result was Scary.
Result #1: With using <CompositeScript>
It didn’t continuous because the Number of failed requests more than 50% of Success requests
Result #2:without using <CompositeScript>
The number of Success requests more than first test
Result #3: Bundling the files Manually into one file or using Web Essentials tool with Visual studio
The result , no comparison between this result and the previous results
So it’s good practice to bundle the files globally one time at the application start by code , manually or by using tools like Web Essentials
(This extension for Visual Studio 2012) https://visualstudiogallery.msdn.microsoft.com/07d54d12-7133-4e15-becb-6f451ea3bea6
(This extension for Visual Studio 2015)