We support Google Analytics default segments and user defined segments.
Segments is a good way to filter you data, you will see one filtered set of data per selected segment. When selecting segments you will automatically get a segment dimension so that you can differentiate between the segments if selecting multiple. This also means that you only can select 7 other dimensions instead of 8.
Selecting overlapping segments will show you a higher overall total while selecting segments without overlap will give you an accurate total for the entire data source. Maintaining the same total in a data source can be a good way to avoid confusion in the future. It's also fine to include overlapping segments but then you have to remember to look at the Segment dimension or filter on Segment when you look at the data.
For example if we have a total of 120 sessions and we select the three segments "Organic traffic", "Desktop users" and "US visitors" we can see these numbers.
If we instead look at two segments that represent the entire user base without overlap we would have an accurate total while still being able to differentiate between different segments.