> Kaeshibashi

The preference is to use a separate pair of communal chopsticks that is not used directly for eating.

> Kosuribashi

I have heard that this one is because it's considered to be an insult implying that the chopsticks are low-quality. (That said, if your chopsticks are indeed low-quality, then avoiding splinters is probably preferable to then visibly plucking splinters out of your fingers.)