If you had two users with a very long password, but the first 100 characters were identical, they'd collide. - Pre-hashing makes this less likely. - Encodi

If you had two users with a very long password, but the first 100 characters were identical, they'd collide. - Pre-hashing makes this less likely. - Encoding the pre-hashed value to prevent NUL bytes is important. But it's a bandaid solution, to be quite honest. We're better served by migrating to Argon2i, which doesn't have these quirks.