Many popular framework provide facilities requiring static imports in your code.
Other than with regular Types, the Eclipse Java Development Tools (JDT) code completion does not work out-of-the-box for statically imported methods.
For example, when writing JUnit Test Cases, you often need to write assert*() methods, matchers, or even fail() methods which must be statically improted. The same applies for the mock up framework Mockito and a lot others.
To enable code completion for those static imports, the Eclipse JDT tooling provides a configuration within the preferences, called Favorites.
You can find them in the workspace preferences following the path:
Window -> Preferences -> Java -> Editor -> Content Assist -> Favorites
Adding the following new types is a good set to start with for JUnit Tests: