While a CNAME implementation does not provide any benefits in terms of cookie lifetime, there may be some other benefits. These benefits include ad blockers and less-common browsers preventing data from being sent to domains they classify as trackers. In these cases, using a CNAME can prevent your data collection from being disrupted for users employing these tools.
In addition, CNAME implementations allow you to choose a custom RDC type which controls where users’ hits are initially routed. The majority of customers do not use custom RDC types.