Right now you cannot isolate and look at traffic that happened before a certain event is set - not even with sequential segmentation. The reason being the top-level segment criteria needs to be set to Hits, but it is not possible to use a hit criteria to reference other hits to exclude/include based on sequence.
Example: I want to analyze pre-conversion traffic (e.g. registration event) and find out average page depth, time spent and so on. Right now I can find out users who converted during their session, but I cannot isolate user behavior that happened after certain event.