Heh, I'm actually using it right now in my prototype, but really just so I could use the same sprite to generate two different effects (normal look and xor). I could always choose another effect, but doesn't matter much to me as my Asus EEE can't run WebGL.
Ultimately I don't know enough to say whether it's needed or not...any artists want to chime in on that note? Still, if it was me I wouldn't out and out remove it; maybe a notice when you export or run layout, like 'warning: you are using the xor effect, which is not supported by WebGL. WebGL users will not see XOR sprite correctly.'