If you’re talking about increasing the number on the supreme court, then you get into a crazy level of one-upsmanship. Each president adds more justices until it becomes entirely unmanageable, with dozens of them, all appointed for life, doing their own thing. Replacing justices who haven’t upheld the highest standards of behaviour, or have, for instance, blatantly taken bribes, should absolutely happen. Hopefully you put in people who don’t fall to those sorts of behaviours, so the opposite party can’t easily replace them.