In my experience, too much of that easily brings in existing biases, too much "this is just how X and I did things at our last company", and sometimes toxicity

In my experience, too much of that easily brings in existing biases, too much "this is just how X and I did things at our last company", and sometimes toxicity from previous companies too. Where I work, interviewers are sent candidates without knowing who is and isn't an employee referral (except for a couple of cases where the candidate has told me or something), and employees who were recommended by another employee statistically perform much better. But we intake a lot of people who just applied too. Referrals are good, but they can't be everything.