Currently the tag bunling option bundles tags that load on all pages with utag.js. While this eliminates some http requests that occur after DOM Ready, it does increase the size of the utag.js file which is loaded before DOM Ready. It therefore negatively impacts performance on the first page where utag.js isn't cashed yet.
What I'd rather see is that tags are bundled based on the load rules applied.
Say you have 5 tags with a load rule "order confirmation page", these tags could be bundled into one utag.n.js file. Eliminating 4 http requests.