SubAssembies provide a very convenient means to co-locate similar or related responsibilities into a single place. For example, it's simple to use a ParsingSubAssembly and a RulesSubAssembly, where the first is responsible solely for parsing incoming Tuple streams (log files for example), and the second applies rules to decide whether a given Tuple should be discarded or marked as bad.

Additionally, in your unit tests you can create a TestAssertionsSubAssembly that simply inlines various ValueAssertions and GroupAssertions. The practice of inlining Assertions directly in your SubAssemblies is also important, but sometimes it makes sense to have more tests outside of the business logic.