Not long ago in Treve we had a Blind slave, and, as I was playing the slaver at the time, it was my job to deal with her. I was very torn about this character, because on the one hand, it had the potential for some Rich and fulfilling RP, with aspects that would both enlighten and amaze, but at the same time, it was so totally Ungorean to me... a Blind slave would have been worthless... she would have cost more to care for that she would ever have gotten in sale, and I think she just would have been killed.
Slaves have one objective assigned them... Do their duty. Be that Screw, Cook, dance, fight, work the fields, whatever. if they CAN'T do their duty, or if it is less efficient to have them doing their duty than not... they are worthless. We as Humans of Earth will take a worthless slave and try to make her fit, because it is Nice of us to try to include them... Good for us... but we are NOT Gorean. we have Not Lived a Gorean life, Not been Raised by Gorean Ideals. Not seen and known slavery as a fact since our birth, and accepted it as a major cultural factor in our development. We dress our Dogs in sweaters and buy expensive litter boxes that attend to our cats. We have a different outlook.... a worthless slave... would have been discarded. Simple as that.
Well, basically, that's my point - I don't think that not being usable for furring would automatically preclude a slave from being kept, but they should be able to do
something. Like, "Baby," the she-urt, she could cook...amazingly. It was her one talent (well, that and calming warriors down, I watched her charm one down and it was incredible!). She did it exceptionally well, and if she had been enslaved, it would make sense for her to be a cook because she was just that good at it. So even though she was non-functional in some aspects of her existence, she could still do one or two things very well.
I remember the Blind slave, Cal, and I think that the issue there was more that the player was unfamiliar with what it was like to be blind. Basically, the slave appeared to exist for the purpose of being comedic humor. She didn't really have any talents other than her sincere willingness to try to help out - but she pretty much always bungled everything. I think if she had some extraordinary talent - like singing, for instance, or a photographic memory, or some such* - that she would have still been valuable enough to keep even if she was a pain in other aspects. Just depends on what you're after.
*she may have had just such a talent, but I didn't RP long enough with her to figure out what, if anything, it was.