The main benefit is indeed being able to identify what resources are 1st and 3rd party accurately when you're looking at performance in the Dynatrace product.
Another good example is in our Dashboarding capabilities we can get a better view of traffic regarding the different sources
There isn't a difference in granularity or information but it's a better way to organize and understand how your resources are affected and where they're coming from.
One additional piece I wanted to add was the ability to count resources used in a user action via USQL.
Take this example:
If we go to a specific User Action and analyze it as well we can get more info on the Resources and their effect on action duration
So back to the purpose of classifying/organizing them - it's just to make sure Dynatrace better reflects your environment and visualization of what's going on