From David Parkinson on Facebook, an expression of his frustration in his German class:
If your language (like English) doesn’t have much inflectional morphology, then learning a language with a respectable amount of it (like German) can be a chore: you have to learn to mark all sorts of distinctions in grammatical categories that don’t come naturally to you.
Many of these inflectional marks are, at least in part, redundant (in a technical sense); they reinforce category distinctions that are marked in other ways. Marks of agreement are like this. So, in German, the definite article agrees in case, gender, and number with its head noun.
Speaking very crudely, these redundant marks are helpful to the hearer, by giving extra cues to relationships among the parts of phrases and clauses. They aid comprehension.
On the other hand, these redundant marks require effort on the part of the speaker, in planning language production and and accessing the appropriate inflectional forms. They work against simplicity.
There are trade-offs here. Redundancy is good. But simplicity is good too.