You’re likely are aware of the recent Google Adwords (AW) remarketing code updates, which are a great new way to manage remarketing segment lists. One of the biggest benefits with this update is the ability to use Google Analytics (GA) to manage your remarketing lists (assuming AW and GA are linked — which they always should be).
With the new remarketing functions, technically you no longer need to use a separate snippet of code for remarketing (the one you get from AW). It can all be done using GA with a slight modification to the Google Analytics tracking code (GATC). This is great from the standpoint of not needing have two separate scripts on the page (e.g. less scripts can help improve page load time).
However, you may want to think twice before you combine your remarketing script with the Google Analytics tracking code (at least for now, until there is a work around for the issue stated below).
At a very high level: The modification to the GATC includes a call to DoubleClick to install third party cookies. Unfortunately, there are browsers and antivirus software with third party cookie blocking settings on by default that stop any scripts with third party cookies from running. Therefore, by having the DoubleClick call in your GATC, any of these browser security functions or antivirus/malware software will stop the GATC from executing, and you’ll lose GA tracking entirely for that visitor. There are reports of 10-75% losses of GA data with this issue.
The crew at Lunametrics has an excellent article with more details on the issue, and a nice work around to figure out how much data you may be losing by combining the AW remarketing script with GATC: http://www.
The very simple way to avoid any data loss issues in Google Analytics is to continue using separate scripts until there is a workaround for this issue (i.e. The AW remarking script is separate from the GA script).