This is definitely a handy new feature in the reporting engine as it can save you time otherwise spent in Excel. Here's what I mean.
Let's say you have many or even several campaigns that are labeled. Prior to the inclusion of labels in the report engine you would have to export these campaigns and tally them up in Excel using Pivot Tables. Not really that hard but takes a bit of time, and any time you can save on reporting is a win.
In the user interface you can filter by campaign label or type and see accurate totals, but if you want to export this you have to pivot the data and weight your performance. The interface weights performance, Excel doesn't do that on it's own.
If you have 2 campaigns with the same label and one has 20 conversions at $100 and another campaign with 5 conversions at $35, an average in Excel would show an average conversion rate of $68 but that's not accurate because it's an average of averages.
You need to factor in the fact that 20 conversions took place with a CPA (cost per action) of $100 so in a spreadsheet that would look like this:
And then you'd need to tally up the rest of your campaign stats in a pivot table. The example above is to demonstrate that you need to do calculations versus averages of averages.
So, if for example you have several campaigns for "Label A" you can now include "Label A" as a roll up in the report. Here's an example with my labels blacked out.