What does it do?
This feature sets Google Analytics to use the advertising features for Demographics and Interests reports. This allows you to:
ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
and is replaced by:
ga.src = ('https:' == document.location.protocol ? 'https://' : 'http://') + 'stats.g.doubleclick.net/dc.js';
Anything to watch out for?
Please note that 'Remarketing' and 'Advertising Reporting' features will need enabling within your Google Analytics account. Details on how to achieve this are available here: https://support.google.com/analytics/answer/2444872?hl=en
Is there a cost for this feature?
Yes, there is an implementation charge of £55 + vat.