It allows you to run individual specs that may have dependencies.  In my experience it's fairly typical for a spec_helper.rb

For example, running the following on master:

    bundle exec rspec spec/grocer/error_response_spec.rb 

fails with:

    1) Grocer::ErrorResponse decoding raises an exception when there are problems decoding
       Failure/Error: raise_error(Grocer::InvalidFormatError)
       NameError:
         uninitialized constant Grocer::InvalidFormatError

because Grocer::InvalidFormatError is defined in lib/grocer.rb, which hasn't been included.  Having the spec_helper.rb include the require for the library under test ensures we don't run into these issues.