Oh no I take that back, it is talking about a specific pattern:
>> Pattern match is redundant
>> In a case alternative: B -> ...
But I do think a better complaint is that you don't need a case expression there at all, but it seems like that's not actually what it's complaining about. Hmm.
My take-away from all this is that, if a case branch can be determined *statically* (i.e., without applying any evaluation steps) not to match, then it is "redundant." If there are counterexamples to this take-away, though, please let me know!
--Todd