I can't see in what sense suffering itself could be positive -- as in, ceteris paribus, better to have suffering than not to.

My favorite pieces of art are mostly very sad. If you could somehow preserve everything else about them while taking away only the tragedy, I'd value them much less. Ceteris paribus, I prefer to live in a world where I can be driven to tears by stories of heroic self-sacrifice (for example).

This is totally irrelevant to the question of animal suffering, though.