[ksaj]

That reminds me of both tonsils and the appendix - two body parts that are often referred to as "useless" even though they probably do some function we're just not aware of.

As for appendix, it seems to be home for bacteria that can cause dementia but are otherwise useful in the gut. I don't know if that's actually its purpose, but if so, it seems pretty important.

[dekhn]

The appendix is vestigial, not useless. It's fair to say it's vestigial, because you can remove it from large numbers of people and they don't die, which is very different from organs like the liver, heart, or lungs.