Broker - Topic - Partition

[kswat]

Hi Axel,
I have a question about Broker - Topic - Partition relationship. Module 3 - Last demo video

In one diagram I had understanding that broker hosts topic. So thought all partitions will be in the broker .
If we have 3 brokers, I thought all 3 brokers will have a copy of partitions. But after re-assign partitions, it looks like partitions are more important than topic i.e. brokers manage partitions than topics.

Can you please tell a scenario where a topic is having 3 partitions and 3 brokers are having b-1 -> P1 , b2 -> P2 , b3 -> P3
Is this possible? What is the advantage /disadvantage .
Is it a simple case of creating reassign script and run ?