Leaves 'em defenseless... against that all-powerful toaster that laughs at her all day! Cats sleep on the couch and they eat cat-food out of the dish. Unless your couch cushion has an aggressive bite, your cat doesn't need to be armed with defenses.
4 cats here, 3 declawed, 1 not, and the cats don't care. They don't know the claws are not there. They don't walk around depressed. They don't walk around in pain. They just go about their lives none-the-wiser.
Seriously, declawing does greater psychological damage to humans than any affect to the cat.