Judges sometimes have to recuse themselves from hearing cases because of financial or personal interests. Some of those conflicts can be spotted in advance, and judges will have standing recusal lists filed with the clerk of the court to keep those cases from being assigned to them in the first place. Of course, these recusals can be weaponized: if there are two judges in a district, and I know that the son of one is a partner at local law firm, I can hire that firm as my co-counsel and ensure that the case will go before the other judge.