Comment by samus

The cases contain actual information that give the speaker more flexibility in structuring their sentences: a German phrase remains syntactically valid as long as you don't move the conjunctions or the verb, while the emphasis of the sentence shifts.

Of course, the German case system has been reduced so far that only the genitive (which is also on its way out) still modifies the noun. Articles have taken up the task of carrying the endings, with only pronouns still being fully declined.

Languages without case systems have other means to achieve this of course.