We've talked a bit about how eDiscovery is similar to Content search. Unlike Content search, once you create a case, eDiscovery will include both search and hold functions:
eDiscovery case home, core (new UI)
Under the new UI, the case will default to Core ED. You can switch to advanced eDiscovery and easily switch back:
eDiscovery case home, advanced (new UI)
As you can see, AED has three levels instead of two and includes a lot of additional features designed to structure complex eDiscovery cases.
Advanced eDiscovery ...
