Why prepare for the behavioral interview?

Most engineers spend weeks on algorithms and about an hour on this round. That gap is the reason preparing for it is worth so much.

This round is scored, not a chat

At most large companies the behavioral interview has its own scoring sheet and its own weight in the decision. It is not a warm-up before the real interviews.

The part people miss is that this round often decides which level you are offered, not only whether you pass. Two candidates can solve the same problems and be offered different titles. One gave concrete evidence of leading work and the other did not.